It’s utterly appropriate in a campaign that of late has been saturated with religion that tonight’s potentially decisive debate is being held on Ash Wednesday. And the Ash Wednesday debate is absolutely critical to Rick Santorum.

Mitt Romney’s campaign has been exceptionally clever in the last week, and Santorum has played into Romney’s hands. It’s striking that conservative Web sites sympathetic to Romney have dumped out all sorts of old videos of Santorum waxing very right-wing on matters such as contraception and the family — and even a sermon he delivered on Satan. Having spent two years covering the Vatican (I even wrote news stories on Satan), Santorum’s talk about the Evil One didn’t surprise me. But it does sound very strange in the context of a presidential campaign.

Never one to run from a fight, Santorum has continued to speak out on these themes, reinforcing his standing as a social and religious conservative so staunch that he would prefer to lose an election than give up on his core beliefs. This has allowed Romney to perform some jujitsu. His fingerprints are not on any of the reports or criticisms of Santorum’s eagerness to run toward the religious right. This has all been handled by surrogates. But Romney has subtly suggested that Santorum is too conservative to beat Obama with such oblique comments as his recent declaration that Santorum has not been “as carefully viewed by the American public” as other candidates. It’s Romney’s invitation to Republican primary voters to take a look at all those videos.

My sense is that Santorum’s social issue extravaganza has put him in danger of losing the Michigan primary. There are plenty of quite conservative Republican women who may now view Santorum as a step too far. They could add to Romney ballots already in the bank from early voting.

How should we think about whether a particular potential third-party candidate is likely to do well?

The conditions for any third party or independent candidate to do well have little to do with the candidate, and a whole lot to do with one factor: whether the president is popular. Almost all of the strong 20th century showings by third-party candidates went along with dismal approval ratings for the incumbent president. But that’s a (sort of) necessary, not a sufficient, condition. After all, lots of people have attempted third-party runs when the president was unpopular, only to wind up as statistical noise.

So how can we tell who is likely to do well if the conditions are right?

The conventional wisdom on this seems to treat it as a question of issues. Thus Thomas Friedman, pushing David Walker, has one set of centrist issues he believes are available to a third-party candidate; National Journal’s Josh Kraushaar disagrees and pushes former House member Virgil Goode on the basis that Goode is pushing a different set of issues.

But I think that’s probably wrong. If we look at Ross Perot, John Anderson, George Wallace, and (going back a ways) Teddy Roosevelt, what history suggests is that success isn’t about issues — it’s about resources. Perot was both wildly rich and had a long history of public action, both of which helped influence the media to take him seriously. Anderson was a presidential candidate in 1980. Wallace was a high-profile governor and had the very best resource of all: a constituency. A real one, not one cobbled together by issues that a columnist or a consultant thinks might get people interested. And, of course, you know all about former president Roosevelt.

Add it all up, and these contenders had one or more of the following: fame, money, political qualifications and a built-in constituency. Near as I can tell, every third-party presidential candidate who took 5 percent or more of the vote was reasonably well known before the campaign (Anderson became well known in losing the nomination). That’s not to say that Walker or Goode couldn’t possibly “succeed” in some way, but neither of them really fits the profile of past successful third-party candidates. The truth is that the way it really works most of the time is someone with a big ego and the resources to make it happen decides to run and probably then fills in whichever issues seem to resonate. Starting with the issues is pretty much getting the whole thing backward. If you want to push some set of issues, try to get a major party candidate to adopt them. It’s a lot easier.

Newt Gingrich loves bombast. He tosses words like hand grenades and Molotov cocktails at people and institutions that run afoul of his worldview. President Obama has been pelted over the years by the historian. But there was something about Monday’s harangue in Oklahoma by Gingrich that could only elicit a “wow” from me. He told students at Oral Roberts University, “Barack Obama is the most dangerous president in modern history.”

The former House Speaker was prattling on about how Obama has offered up the U. S. of A. on an altar to “radical Islamists.”

Across the planet today, the forces of religious repression are on the march and this administration has intellectually disarmed. It has morally disarmed. It is incapable of describing what threatens us.. . .

The president wants to unilaterally weaken the United States. He wants to cut the aid to Israel for its anti-ballistic missile defense. He refuses to take Iran seriously. We are in a world that is very dangerous. And I say this to those of you who represent the next generation because you’re going to bear the consequences. We are really at risk someday in your lifetime of losing an American city. . . .

So, defeating Barack Obama becomes, in fact, a duty of national security because the fact is that he is incapable of defending the United States.

Gingrich will say anything to get attention. The redder the meat, the bigger the hand grenade the better, it seems. And, as is his wont, Gingrich goes too far. God forbid some unstable soul thinks it is his or her duty in the name of national security to preempt the ballot box. But any notion that Obama is incapable of defending the United States — or even unwilling to do so — was put to bed on May 1, 2011.

Listening to the rhetorical red meat spewed by Rick Santorum over the weekend, I was reminded of the opening paragraph of a story by The Post’s Karen Tumulty from earlier this month. “The playbook for Republican presidential contenders goes at least as far back as Richard Nixon,” she wrote. “Run hard to the right in the primaries; steer back to the center for the general election.” Her piece was about the trouble Mitt Romney might have were he the nominee. Now that Santorum is poised to become a certified frontrunner, I find myself wondering if he would have the same trouble.

What Santorum and Rommney are doing is not a uniquely Republican strategy. Democrats do it, too. Like its far-right brethren in the GOP, the far left is the energy and lifeblood of the Democratic Party. You’ve got to win them over to get the nomination. But I’m convinced that Santorum’s comments of late go so far to the right that, even if he were to pivot back towards the center, he’d still be too far right for a nation that likes its leaders to hug the center as much as possible.

Peter Gleick violated a principle rule of the global-warming debate: Climate scientists must be better than their opponents.

Gleick, the president of the Pacific Institute for Studies in Development, Environment and Security, admitted Monday night that he dishonestly obtained fundraising and strategy documents from the Heartland Institute, an obnoxious anti-climate science think tank. In the process, he’s done more to discredit himself and his work than he has to expose cynicism and collusion among global-warming deniers.

It’s very tempting for scientists and their allies to employ to tactics of their over-aggressive critics. Yet the global warming camp must make an affirmative case for ambitious action on carbon emissions. Critics need only poke holes in the scientists’ arguments, or, as is so often the case in global warming debates, merely insist they’ve done so. Manipulation and perfidy work much better for the deniers.

Whatever the misdeeds of those who attack climate research, however braindead the opposition to climate scientists appears to be, advocates degrade themselves when they allow their frustrations to get the better of their ethical responsibilities. They lend credence to the (wrong) impression that both sides of the debate are equally worthy of criticism, that global warming is another ideological war that both sides fight deceitfully. In that context, those who want to spend lots of money to green the economy lose, and those who want to do nothing win. As Rick Santorum tours the country accusing climate activists of treachery and conspiracy, this should be only more obvious.