The GOP Senate victories of 2010 have made Republicans hungry for additional gains. On paper, they enjoy a big advantage in 2012, because only ten of their seats are up for election, compared with 23 seats of senators who caucus with the Democrats. The GOP is especially eager to seize pickup opportunities in right-leaning states such as Montana, Nebraska, and North Dakota.

Before any red-state Republican can go on the attack, however, a few may find themselves playing defense. If 2010 holds any lesson for incumbents, it’s that conservative voters are willing to mutiny against moderates. Two Republican senators, Robert Bennett of Utah and Lisa Murkowski of Alaska, fell to primary challengers. A third, Arlen Specter of Pennsylvania, chose to switch parties rather than face GOP voters. All were victims of rivals who harnessed the energies of the Tea Party movement, whose influence is more likely to grow than shrink over the next two years.

At least four Republican senators already must worry about renomination in 2012: Richard Lugar of Indiana, Kay Bailey Hutchison of Texas, Orrin Hatch of Utah, and John Ensign of Nevada. Three confront questions about their devotion to conservative principles and the fourth must overcome doubts about his effectiveness and electability. All will likely face credible primary challengers.

A couple of weeks after the 2010 elections, Richard Lugar released a poll to demonstrate his formidability as he seeks a seventh term. It portrayed him as Indiana’s most popular politician, putting his favorability rating at 66 percent — slightly higher than even that of Gov. Mitch Daniels, who is often mentioned as presidential timber. The numbers made the 78-year-old Lugar look like a shoo-in for reelection.

Except that the poll also gave off a whiff of weakness: It tested the popularity of two Indiana Republicans, state senator Mike Delph and state treasurer Richard Mourdock. Their favorability ratings barely registered. Most voters don’t know much about them. By including them in his poll, however, Lugar revealed that he’s anxious to keep tabs on possible primary foes.

Both men are thinking about running against Lugar for the GOP nomination. “People started calling me about it back in September,” says Mourdock. “My response was: ‘What did I ever do to you?’” Since then, however, Mourdock has won reelection to his statewide office with 62 percent of the vote. Then Lugar became one of just eight Republican senators to vote against a ban on earmarks. “That vote showed how much he has drifted away from Hoosier values,” says Mourdock. “Even Evan Bayh voted the right way — and he’s a Democrat.” Bayh is Indiana’s retiring junior senator.

The vote on earmarks is not Lugar’s only post-election apostasy. During the Senate’s lame-duck session, he called for passage of the DREAM Act, which would provide amnesty for illegal aliens who attend college or join the military. More significantly, Lugar has used his position as ranking member of the Senate Foreign Relations Committee to crusade for the New START treaty with Russia. Collaborating with the Obama administration, he has tried to push the pact through the Senate before a strengthened and skeptical GOP caucus can get its hands on the agreement in 2011.

These endeavors earned Lugar one of those soft profiles that the New York Times likes to lavish on Republicans who defy conservatives: Lugar, wrote reporter Jennifer Steinhauer, “is standing against his party on a number of significant issues at a politically dangerous time to do so.” The American Conservative Union gives Lugar a lifetime rating of 77 percent, which makes him one of the GOP’s more liberal senators.

State senator Delph says that his serious frustrations with Lugar go back at least as far as the nomination of Elena Kagan to the Supreme Court. Lugar was one of five Republicans who voted to confirm her. “She’s the most liberal justice of my lifetime,” says Delph. “Conservatives should be outraged by her support for partial-birth abortion, but Lugar chose to ignore it.”

In the last election cycle, a former congressman who went on to head the Club for Growth, a political-action committee that supports economic conservatives, ousted a moderate Republican senator: In Pennsylvania, Pat Toomey drove Arlen Specter out of the GOP and then captured the seat Specter had occupied for three decades. Today, the president of the Club for Growth is Chris Chocola, a former congressman from Indiana who questions Lugar’s conservatism. Chocola says he has no interest in running for anything: “I’ve been cured of all political ambition.” Yet he won’t rule out the possibility that his organization will finance one of Lugar’s competitors in a primary. “If Senator Lugar retires, he’ll go down in history as a great statesman,” says Chocola. “But I don’t think he’ll retire, so we’ll see what happens.”

#page#For conservatives, one of the most exciting Senate races of 2010 took place in Florida, where 39-year-old Cuban-American lawyer Marco Rubio had the gumption to battle a darling of the Republican establishment, the state’s governor, Charlie Crist. Texas isn’t Florida, but its next Senate race may feature a young Cuban-American lawyer and conservative favorite — Ted Cruz — against a moderate Republican, Sen. Kay Bailey Hutchison, who is widely perceived as vulnerable to a challenge from within her party.

Right now, Cruz isn’t a declared candidate. Neither is Hutchison: She’s not saying whether she plans to pursue reelection. For Cruz, it may not matter. He appears to be getting ready for a campaign, whether it’s against her or for an open seat.

Weakness is provocative — and Hutchison’s weakness became obvious when she took on incumbent governor Rick Perry in a GOP primary this year. At first, their contest looked like it would become a prizefight between two Texas titans. But Perry delivered a decisive knockout. Hutchison finished closer to third place than first.

“One of our strategies during the primary was to remind Texas Republicans that Hutchison is more of a moderate than a conservative,” says a veteran of the Perry team. “She can’t be dismissed, especially as an incumbent, but Tea Party voters will remember her record and they may want to look elsewhere for leadership.” The Perry campaign slapped a memorable nickname on the senator: Kay Bailout Hutchison.

Hutchison may have hurt her chances in other ways as well. During her bid for the governorship, she promised to resign her Senate seat so that she could focus on her campaign. Yet she never got around to giving up her office. Following the loss to Perry, she announced that, on second thought, she would keep it. Suddenly, she appeared both beatable in a GOP primary and something other than a straight shooter.

The pledge to resign had allowed several Republicans to envision themselves in her Senate seat, and they began to explore campaigns. Many conservatives prepared to get behind Michael Williams, a bald, bow-tie-wearing African American who has been elected three times to the state railroad commission, an influential agency that regulates the energy industry. He drew the support of Sen. Jim DeMint, the South Carolina Republican whose political-action committee, the Senate Conservatives Fund, shaped a few 2010 races. DeMint has said he doesn’t plan to endorse any 2012 candidates who take on incumbent Republicans. If Hutchison announces her retirement, however, Williams probably can count on DeMint’s early backing.

No matter what Hutchison does, there may be a logjam of primary candidates — not just Cruz and Williams, but also railroad commissioner Elizabeth Ames Jones, former secretary of state Roger Williams, and Lt. Gov. David Dewhurst, who will probably be the most significant contender if he runs. Dewhurst has the ability to self-fund and the support of Austin’s political establishment; the conventional wisdom will hold that the race is his to lose. But conservatives will harbor doubts because they don’t consider Dewhurst one of their own. It’s possible to imagine an overconfident Dewhurst playing the role of Crist to Cruz’s Rubio.

The GOP nomination process in Utah is tailor-made for insurgents, as Republican senator Robert Bennett learned the hard way this year. At a party convention in May, he finished third. His opponents succeeded in portraying him as a Washington insider who had lost touch with conservatives back home. One of them, Mike Lee, strolled to victory in November.

So Utah conservatives immediately started to wonder: Is Orrin Hatch next? He’s more conservative than Bennett. He also possesses better political skills. But he may have to face a foe who is much better known than Lee was at this point in the last election cycle: Republican congressman Jason Chaffetz. The 43-year-old speaks openly about trying to nab the nomination. “I’m a definite maybe,” he says. “Hatch has been a great senator, but he’s asking voters to keep him in office for 42 years, until he’s 84.”

Chaffetz insists that his campaign would amount to more than a youth revolt against an aging incumbent. It would include a long list of policy complaints. “Hatch voted to bail out the financial markets and expand the S-CHIP health-care program,” says Chaffetz. “What’s conservative about that?” Pro-lifers regard Hatch as an ally on many fronts, but note with regret that he has favored the federal funding of stem-cell research that destroys human embryos.

#page#Bennett’s failure to win renomination isn’t the only bit of recent history that should trouble Hatch. There’s also the way in which Chaffetz won election to Congress in 2008: He beat Chris Cannon, a six-term incumbent, by running an issues-driven race and taking advantage of Utah’s peculiar nominating rules, which emphasize personal connections with party activists. “I did it once and I can do it again,” says Chaffetz. “I was a Tea Party candidate before there was a Tea Party.”

The issue that energized Chaffetz and his supporters two years ago was immigration. Cannon was an outspoken backer of President Bush’s proposal to offer amnesty to illegal aliens and create a new guest-worker program. Chaffetz opposed the whole package. Hatch doesn’t provide quite as big a target for conservative ire, but Chaffetz is quick to point out that the senator was for the DREAM Act before he was against it. Hatch can throw a few punches of his own: Chaffetz is a critic of the war in Afghanistan, a position that could give pause to Republicans who want to fight an aggressive war on terror.

The main problem for Chaffetz may be that few Utah Republicans see Hatch as just another Bennett. “People like Orrin a lot,” says Jim Hansen, a retired congressman who endorsed Lee over Bennett this year but plans to stick with Hatch. “If you have a ditch problem on your ranch and the federal government is harassing you, Orrin will jump right on it. People appreciate that.” Former governor Norm Bangerter also supported Lee in 2010 and insists he’ll be with Hatch in 2012.

But it’s early to bet against Chaffetz. He says he’s in no hurry to make up his mind, and Utah Republicans still have a lot of time to make up theirs.

On November 19, Nevada Republicans met in rural Fallon. The weather was bad, but almost 200 people attended, including Governor-elect Brian Sandoval and the recently defeated Senate candidate Sharron Angle. Sen. John Ensign, however, didn’t show. “When it was announced that he wouldn’t be there, people were disgusted — and a bunch of them actually clapped,” says Heidi Smith, a Republican National Committee member. “Later on, I spoke to a breakout group of maybe 30 or 40 people. I asked, ‘How many of you will vote for John Ensign?’ Nobody raised a hand.”

The rap on Lugar, Hutchison, and Hatch is that they’re not conservative enough for red-state Republicans. Nobody says the same about John Ensign. The American Conservative Union gives him a lifetime rating of 94 percent. Yet he’ll have a difficult time in 2012.

Last year, Ensign confessed to an extramarital affair with an aide. The problem worsened with the revelation that his parents had paid $96,000 to the woman’s husband. Several investigations ensued. Although Ensign has not yet been charged with any legal wrongdoing, the scandal has dimmed his once-bright future. He quit as head of the Republican Policy Committee, the fourth-ranking post in the Senate GOP leadership. “He is a walking political corpse,” wrote Jon Ralston of the Las Vegas Sun on November 10.

Can he rise from the dead? “People have come back from worse, but he won’t have an easy reelection,” says Ryan Erwin, former executive director of the Nevada GOP. “I’m certain he’ll face a primary challenge.” The most talked-about potential candidate is Dean Heller, a congressman who refuses to comment on his plans for 2012 — which is another way of saying he hasn’t ruled out running against Ensign. There’s also Brian Krolicki, the lieutenant governor. The wild card is Angle, the woman who failed to knock off Democratic senator and majority leader Harry Reid this year. “Don’t underestimate her,” warns Sue Lowden, who ran against Angle for this year’s GOP Senate nomination. “She would be a very serious candidate, especially in a primary.” Lowden says she would run her own campaign for the Senate in 2012 only if Ensign stepped aside first.

Even in freewheeling Nevada, pols can pay a price for their sins. In this year’s GOP gubernatorial primary, Sandoval defeated incumbent Jim Gibbons partly because of Gibbons’s messy personal life, which recently involved a divorce.

Ensign and his wife remain together, but in politics, that guarantees nothing. Nevada is a toss-up state, and Democratic congresswoman Shelley Berkley may bid for the Senate. Many Republicans fear that a showdown between Ensign and Berkley would create the best chance for Democrats to pick up a seat now held by the GOP. So any Republican who challenges Ensign will be able to deliver a simple but compelling message: The senator can’t win.

And for many conservatives who hope that 2012 will realize the promise of 2010, winning is the only thing.