Republican presidential contender Rick Santorum has his share of problems stemming from his sincerely held but extreme views on a number of issues and his penchant for inflammatory rhetoric that makes even commonplace observations sound loony. (Yesterday, for example, he made the bizarre accusation: “President Obama once said he wants everybody in America to go to college. What a snob.” If there was a point about the flaws in the goal for everyone to attend college, it was hidden under a bushel of senseless rhetoric.)

But in Wednesday’s debate, a more fundamental problem was on display: Santorum was a senator.

A sharp reader, William from Delaware, e-mails me: “The GOP should never nominate a senator for president. In post WW II America, whenever the GOP nominates a senator (Goldwater, Dole, McCain), they lose. Whenever the GOP nominates a governor (Reagan, Bush 43) or a vice president (Nixon, Bush 41), they win the presidency. Why? First, the American people are looking for executive leadership from a governor or VP – not a DC insider from Capitol Hill. Second, each of these GOP senators carries the burden of a congressional voting record that is distorted and picked to death. Where David Axelrod leaves off, the MSM will continue the assault.”

Because Santorum cast himself as a more pristine conservative than his opponents, he made it that much more inviting to use his voting record against him. Jay Cost of the Weekly Standard observes: “Much of what Congress does can be chalked up to members trying to get reelected, and that means sending the bacon back home to the district. But it would be politically impractical for members to put specific items up for a vote one-by-one, so they group them all together, so that everybody votes for your pork and you vote for everybody else’s pork simultaneously. Thus, Santorum never got to choose between ‘good’ earmarks and ‘bad’ earmarks — he had to vote for all or none.”

In essence, Santorum took a problematic Senate voting record and turned it into a hypocrisy problem. Had he not posed as someone who would not stoop to compromise his ideological convictions, the votes for Big Labor, earmarks, No Child Left Behind, Medicare Part D and the Bridge to Nowhere wouldn’t look quite as bad.

It is for this reason that his alliance with former senator Arlen Specter also is so problematic. It is not just his endorsement of Specter’s reelection in 2004, but his presidential support in 1996 that is a killer. In the C-SPAN video from the Specter kickoff, we can see Santorum sitting right up front applauding the candidate who proclaims (beginning at about the 4:45-minute mark) that he is running “to champion tolerance and freedom, especially a woman’s right to choose.” Santorum cheers for a candidate characterizing himself as a “social libertarian.”

You can chalk up that display to political back-scratching. Specter had lent considerable help and even some staff to Santorum for his Senate run in 1994. So Santorum was willing to return the favor by pushing the candidacy of a man who opposed Santorum’s core principles. It happens. But for Santorum it’s jarringly inconsistent with his message.

Santorum unfortunately underestimated the degree to which his record and past political behavior could be used to undermine his self-image a a doctrinaire conservative. It appears that he didn’t order opposition research on himself and was unprepared for the kind of scrutiny you get in the New Media age when every reporter and campaign staffer can find reams of data with no more than a Google search.

Any lawmaker has a problem with votes that don’t later match up with his campaign theme. But Sen. John McCain (R-Ariz.) ran as a maverick in 2008, not as a holier-than-thou conservative. In that case his votes were irksome to the right, but they did not reveal him to be a “fake,” in Rep. Ron Paul’s vernacular.

In the past couple of weeks Santorum has lost much of his luster as the more conservative alternative to Romney while simultaneously demonstrating that he will turn off women, moderates, suburbanites and less religious voters in a general election. That’s not easy to do. But when rhetorical extremism collides with a very mixed Senate record, it’s not pretty. You get what we saw last week: a campaign crack-up.