William Galston, the issues director of Walter Mondale’s 1984 presidential campaign, takes a look at President Obama’s reelection prospects and finds that he’s vulnerable to a “credible” Republican challenger. Given the economy, I don’t think this is news, but the question is whether the Republicans can produce a credible challenger. Galston acknowledges the possibility that the GOP won’t field a credible candidate but he doesn’t really examine the likelihood.

If the Republicans nominate someone who’s seen by the people as a plausible potential president, they’re going to be in the game unless the economy surges as it did in 1984. But they have two opportunities to commit creedal suicide: They could nominate someone too far outside the mainstream to compete effectively, as they did in 1964, or their primary electorate could force more mainstream aspirants to adopt positions that would cripple their general election chances.

I think we’ve already seen evidence that the Republicans are adopting positions that will cripple their general election chances. The first indicator is coming from the governor’s mansions in Madison, Lansing, Harrisburg, Tallahassee, Augusta, Phoenix, and Columbus. The new batch of Republican governors are collectively overreaching in a big way and causing a major backlash. Usually, you would see it as advantageous to own the governorships in swing states, but I don’t think that will be the case in 2012.

Another indicator in the willingness of Congressional Republicans to get behind Rep. Paul Ryan’s budget plan which was easily eviscerated by the president in his budget speech on Wednesday. It would be one thing if the GOP could actually enact these reforms and take credit for tackling our long-term budget concerns, but they won’t have the benefit of accomplishing anything remotely like what they have proposed. Instead, nearly every member of their caucuses has cast a vote in favor of destroying Medicare and slashing taxes on millionaires and billionaires. None of their presidential aspirants came out against Ryan’s plan and it is unlikely that any of them will.

While we all cringe at the spectacle of Donald Trump questioning the president’s citizenship, Mitt Romney felt compelled to vouch for Obama’s legitimacy. With candidates like Newt Gingrich, Sarah Palin, Michele Bachmann, Rick Santorum, and Ron Paul, the debates will be a freak show even without The Donald.

There are only two candidates (Mitt Romney and Tim Pawlenty) who can reasonably be considered “credible” and they have real weaknesses. Regardless of whatever positions individual candidates take on various issues, the one rock-solid article of faith issue that all Republicans will have to agree on is that Obama’s Affordable Care Act must be repealed. In 2008, I think Obama and Clinton competed in nineteen debates. If Mitt Romney has to defend his signature health care bill in Massachusetts (which was a model for Obama’s bill) nineteen times, he’s going to lose.

As for Pawlenty, he strikes me as an implausible leader who lacks charisma and any compelling argument for being the standard-bearer of conservatives. His main attraction may be a perceived but unproven “electability” advantage.

And, in any case, given where the Republicans have positioned themselves right now, I can’t see Romney or Pawlenty winning the nomination and still maintaining any independence from Rush Limbaugh-orthodoxy.

The weakness of the Republican field is not going unnoticed by Republican lawmakers, but Ed Kilgore argues persuasively that relying on some dark-horse savior is probably not a good idea.

Personally, I don’t see anyone with the fire-in-the-gut needed to win the Republican nomination, let alone the presidency.

Presidential prognosticators like to look at things like the unemployment rate and economic growth to predict outcomes. That’s a good place to start, but sometimes a party nominates someone who has no chance of winning regardless of economic conditions. What’s odd about the current situation is that the Republicans don’t seem to have any candidate who can simultaneously appeal to their base and to the general electorate.

I’m not saying the presidential election will be a cakewalk, but it’s hard to see how it could possibly be competitive. And that’s why Nate Silver is right that the Senate is not necessarily lost.