It’s funny: In so many cases in last night’s Republican debate in Arizona, Rick Santorum gave more direct and less politically-driven answers than Mitt Romney offered. Yet Santorum’s replies were complicated and kept putting him on the defensive.

The discussion among the GOP candidates on earmarks was fascinating. After months and months in which all Republicans regularly bashed earmarks, each of the candidates — including libertarian Ron Paul — defended particular earmarks that they had sought for particular purposes. Never has an exchange so underscored how sweeping, popular rhetoric is usually misleading about what candidates actually think, and do.

Santorum gave a lengthy answer in which he explained why he had sought earmarks for Pennsylvania, and why, when earmarks began to be abused, he called for their abolition. He also made an entirely valid point: Romney has attacked him for pursuing earmarks even as Romney himself sought federal help, through earmarks, for the Salt Lake City Olympics and projects in Massachusetts.

Romney didn’t bother to the earmarks he had sought and just repeated his rhetorical salvos against the earmark process. The audience seemed to like Romney’s answer better.

Santorum’s problem is that what he said could be too easily parodied as a claim that he had been for earmarks before he was against them. That would unfair, of course, but sometimes complexity is simultaneously (1.) more accurate and candid, and (2.) not terribly effective politically.

You’re not going to believe this, but tonight’s debate in Arizona will be the 26th for the remaining candidates for the Republican nomination. Rather than bore us to death, the debates have been been exciting and terrifying. And they have been the vehicle used by Mitt Romney, Rick Santorum, Newt Gingrich and Ron Paul to make a splash or catapult to front-runner status. Tonight will be no different.

Momentum is on Santorum’s side. Even though he’s caused quite a stir in the national press with past and present comments on theology, contraception, neonatal care and Satan, the controversy only seems to have helped him with primary voters. Santorum’s task tonight is to ensure the wave keeps rolling after tonight. And it could all depend on how he defends his positions on those issues. If you don’t think such answers matter, just ask Gov. Rick Perry about his “you don’t have a heart” retort on immigration from his very first debate. To his credit, Santorum has been rather good in the debates. Of course, he was a second-tier candidate. Tonight, the bull’s eye is on him.

The NBC News-Marist poll of Michigan voters released this morning is fascinating. There’s no other way to describe it. And there are three areas I found most intriguing: President Obama’s job approval rating; the view of the auto bailout;  and the tension between what Republicans surveyed say they believe and what they actually want.

The unemployment rate for Michigan was 9.3 percent in December, the most recent data available. The national unemployment rate then was 8.5 percent. Today, it is now 8.3 percent. Michigan has seen more than its share of economic misery over the past decade, none more worrisome than the near implosion of the auto industry. That’s why I was surprised to see the president hold a 51 percent approval rating in the Wolverine State.

Then again, perhaps I shouldn’t have. After all, just like every Democrat since 1992, Obama carried Michigan. And he did so by 16 points in 2008. But there’s no doubt that the state’s improving economic fortunes are playing a role. Two weeks ago, I cheered Michigan’s first budget surplus in a decade. Gov. Rick Snyder (R) got to this firm financial position in part by whacking the middle class and working poor. Then, last week General Motors announced $7.6 billion in profits for 2011, the highest in its history. Not only that, in March, the company will send 47,500 blue-collar workers a profit-sharing check of $7,000.

All of this was made possible by the auto bailout begun by then-President George W. Bush in the waning days of his administration and continued by Obama. But NBC-Marist poll reveals somewhat mixed emotions about it.

Overall, do you think the bailout of the auto industry was a good idea or a bad idea?

                            Registered Voters      Likely Voters

Good idea                 63                          42
Bad idea                     28                          50

The saving of Detroit is a big hit among registered voters across the state (63 to 28). Not so much among likely voters in Tuesday’s Republican primary. While 42 percent of them think the auto bailout was a “good idea,” 50 percent agreed it was a “bad idea.” And if you want to understand the depths of the loathing, when asked if Obama deserved credit for the auto-industry  turnaround a whopping 69 percent of likely voters said “not very much/no credit at all.” That might explain why Mitt Romney and Rick Santorum have been vocal in their opposition to the auto bailout despite its benefit.

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.