The Republicans swept November’s midterm election by making it highly ideological, a referendum on two years of hyper-liberalism — of arrogant, overreaching, intrusive government drowning in debt and running deficits of $1.5 trillion annually. It’s not complicated. To govern from the left in a center-right country where four out of five citizens are non-liberal is a prescription for electoral defeat.

Which suggested an obvious Republican strategy for 2012: Recapitulate 2010. Keep it ideological. Choose a presidential nominee who can best make the case.

Last month, Democrats turned the race for the 26th congressional district of New York into a referendum on Medicare, and more specifically on the Paul Ryan plan for reforming it. The Republicans lost the seat — after having held it for more than four decades.

Problem was, their candidate was weak, defensive, unschooled, and unskilled in dealing with the issue. Republicans have a year to cure that. If they can train their candidates to be just half as fluent as Ryan in defending their Medicare plan, they would be able to neutralize the issue.

But that in and of itself is a tactical victory for Democrats. Republicans are on the defensive. Democratic cynicism has worked. By deciding to do nothing about debt and entitlements, and instead to simply accuse Republicans of tossing granny off a cliff, they have given themselves an issue.

And more than just an issue. It gives President Obama the perfect opportunity to reposition himself to the center. After his midterm shellacking, he began the (ostensible) move: appointing moderates such as William Daley to high White House positions; making pro-business, anti-regulatory noises; even offering last month a token relaxation of his hard line against oil drilling.

Ostentatious but not very convincing. Now, however, the Obama pitch is stronger: Leftist? On the contrary, I bestride the center like a colossus, protecting Medicare from Republican right-wing social engineering.

It’s not that the ideological case against Obama cannot be made. Obamacare with its individual mandate remains unpopular. The near-trillion-dollar stimulus remains an albatross. Even the failed attempt at cap-and-trade — government control of energy pricing — shows Obama’s determination to fundamentally transform America. And he is sure to try again to complete his coveted European-style social-democratic project if you give him four more years.

Medicare has nonetheless partially blunted that line of ideological attack. Yet, just as the Democrats were rejoicing in the fruits of their cynicism, in came the latest economic numbers. They were awful. Housing-price declines were the worst since the 1930s. Unemployment rising again. Underemployment disastrously high. And as for chronic unemployment, the average time for finding a new job is now 40 weeks, the highest ever recorded. These numbers gravely undermine Obama’s story line that we’re in a recovery, just a bit slow and bumpy.

Suddenly, the election theme has changed. The Republican line in 2010 was: He’s a leftist. Now it is: He’s a failure. The issue is shifting from ideology to stewardship.

As in 1992, it’s the economy, with everything else a distant second. The economic numbers explain why Obama’s job approval has fallen, why the bin Laden bump disappeared so quickly, and why Mitt Romney is running even with the president. Romney is the candidate least able to carry the ideological attack against Obama — exhibit A of Obama’s hyper-liberalism is Obamacare, and Romney cannot rid himself of the similar plan he gave Massachusetts. But when it comes to being solid on economics, competent in business, and highly experienced in governance, Romney is the prohibitive front-runner.

The changing nature of the campaign is also a boost for Tim Pawlenty, the successful two-term governor of a very liberal state, and possibly for another ex-governor, Jon Huntsman, depending on who he decides to run as.

Nonetheless, despite the changed conditions, I would still prefer to see the Republican challenger make 2012 a decisive choice between two distinct visions of government. We are in the midst of a once-in-a-generation debate about the nature of the welfare state (entitlement versus safety net) and, indeed, of the social contract between citizen and state (e.g., whether Congress can mandate — compel — you to purchase whatever it wills). Let’s finish that debate. Start with Obama’s abysmal stewardship, root it in his out-of-touch social-democratic ideology, and win. That would create the strongest mandate for conservative governance since the Reagan era.

— Charles Krauthammer is a nationally syndicated columnist. © 2011 the Washington Post Writers Group.