As Barack Obama’s cavalcade of dramatic post-primary position changes advanced, he momentarily threw off his detractors.

Just who was this guy? A naïve idealist who would promise a complete withdrawal from Iraq in less than a year and a half, would hold a summit with Ahmadinejad without preconditions, unilaterally withdraw from NAFTA, and oppose any development of additional nuclear power plants? Or a ruthlessly flexible pragmatist, who would adjust his Iraq plan to circumstances, demand vague “preparations” before meeting dictators, dismiss his previous NAFTA rhetoric as “overheated,” and declare that nuclear power has to be “part of the mix”?

We may have our answer soon. If Obama selects Virginia Governor Tim Kaine as his running mate, he might as well write “NAÏVE IDEALIST” in fireworks above the announcement ceremony.

Democrats and Obama’s allies would inevitably do their best to put the finest lipstick on the oinker of a Kaine selection. But it would be a catastrophic mistake politically and a fascinating window into how faulty Obama’s decision making is.

Since he clinched the nomination, the criticism of Obama that has gained the most traction is the question, “Is he ready?” Americans generally like Obama, and he polls well on almost all of the big issues this year. The two poll questions he collapses on are, “who has more knowledge and experience to be president?” and “which candidate would be a good commander-in-chief?”

Obama has repeatedly said that he doesn’t see those questions as his weaknesses, and he doesn’t feel any particular need to have a running mate with strengths in those areas. A selection of Kaine would show he means it, and would be an implicit message to voters: Take those concerns and go pound sand. You have to look really hard to find a potential veep with less time as a senator or governor than Obama, but Kaine is one of them. Kaine has been governor for about two and a half years; Obama has been a senator about three and a half years. Rather than broaden the ticket’s breadth of knowledge, Kaine’s greatest areas of expertise are probably urban issues (as former mayor of Richmond) and civil-rights law (from his private practice) — the two areas Obama probably knows most about.

There have been plenty of missteps in other areas. A columnist for Kaine’s hometown paper labels him “naif on diplomacy, defense and the national economy”; the news pages write that his “enthusiasm, however, cannot mask a record as governor that even Democrats describe as mixed.” Transportation issues have been the biggest disappointment, and while the presence of illegal immigrants has stirred furious passions in his state and spurred the creation of local ordinances cracking down on employing them, Kaine created a commission to “study the costs and benefits that immigration is having on the Commonwealth.”

His official gubernatorial biography touts the state remaining on Forbes’s list of the most business-friendly states in America, but the state dropped out of Forbes’s top ten in business costs and economic climate during Kaine’s tenure.

Obama and Kaine would be the most inexperienced pair to hit Washington in modern history. Then-one-term-governor Jimmy Carter at least had Walter Mondale, who had been a senator for 12 years. Bill Clinton and Al Gore look like seasoned old pros by comparison.

And despite different backgrounds, Obama and Kaine have odd similarities. Not only did both attend Harvard Law School, but both of their wives did as well. The nominee whose political career began in 1996 would have a running mate whose career began in 1994. Both men advanced to higher office when the finger of fate poked their rivals in the eye: A top rival for Kaine’s mayoral bid lost a preceding city-council reelection campaign by a handful of votes; the woman who probably would have beaten him in the primary for lieutenant governor in 2001 was diagnosed with terminal cancer.

Still, Vice President Kaine would have some glaring issue differences with the president he would serve. Running for governor in 2005, Kaine pledged to pass “an enforceable ban on partial-birth abortion” and to promote “abstinence-focused education.” He doesn’t support “criminalizing women and doctors,” but it’s safe to say he would have more deviations from the NARAL line than any other Democrat on the party’s ticket in many years.

Kaine opposes offshore drilling for oil, but says he’s amenable to exploring for offshore natural gas. (A drilling proponent might take that deal, let the oil get discovered, and then revisit the issue of the ban once frustrated motorists learn that oil deposits are sitting off their shores.) He’s tentatively open to a new uranium mine in his state, which infuriates local environmentalists.

The most-often-cited justification for a selection of Kaine is that he would help Obama win Virginia in November. While probably true, there’s been little sign of Virginians thrilling at the thought of their governor being a heartbeat away from the presidency.

A late June poll by Survey USA had Obama two percent ahead of McCain in Virginia. With Kaine as his running mate, matched up against McCain/Bloomberg, McCain/Jindal, and McCain/Fiorina, Obama was . . . still ahead by 2 percent in each matchup. Kaine’s popularity is probably the most localized of any of Obama’s options; SurveyUSA’s poll in Missouri at the same time found Kaine the weakest of veep options that they polled.

It’s easy to picture a scenario in which Obama wins the presidency without Virginia, but an Obama-Kaine ticket would turn the commonwealth into a must-win state.

Since his victory, Kaine has often been seen as a poor man’s Mark Warner, his popular predecessor as governor. During an appearance for Kaine in 2005, Obama made his pitch as, “you have the opportunity in this election to carry on a legacy that has become the envy of every other state in the nation” — a statement that says more about the departing governor than the aspiring candidate.

Warner, very likely to win his bid for the U.S. Senate this year, has denied any interest in being Obama’s running mate. But perhaps the Democratic nominee ought not to settle. If Obama went to Warner and said, “I know you’ve been working hard and planning on serving in the Senate, but I need you by my side as I lead the country,” could Warner bring himself to say no? Would he pick an almost-automatic six years in the Senate over at least four years as President Obama’s right-hand man? – Jim Geraghty writes “The Campaign Spot” blog on NRO.