This is how primary campaigns end — not with a bang but with a wimper. Or, more accurately, a whine.

Rick Santorum lost his temper with the New York Times’ Jeff Zeleny on Sunday when Zeleny, perhaps the most even-tempered reporter we know, pushed the former Pennsylvania Senator on his remark that former Massachusetts governor Mitt Romney would be the “worst Republican” to nominate against President Obama .

“Quit distorting my words. It’s bulls---,” Santorum said to Zeleny, insisting that he was referring only to Romney’s health care positioning not to the candidate more broadly.

That, of course, is a distinction without a difference. And Santorum knows it.

It’s the latest in a series of head-scratchers from Santorum — make sure to check out his “Are you kidding me?” riff from late last week — and former House Speaker Newt Gingrich over the past week or so, a familiar pattern that typifies the final throes of candidates virtually certain to come up short in the primary. (Gingrich’s latest outburst came on Friday when he called President Obama’s remarks about slain Florida teenager Trayvon Martin “disgraceful”.)

“What we’re seeing are signs that the nomination battle is effectively over,” said John Weaver, who served as a senior adviser to the presidential bid of former Utah governor Jon Huntsman. “The lashing out at the media and grasping of straws, as in Newt’s comments about the killing of Trayvon Martin, are indicators we’ve entered the walking dead period.”

The simple fact is that these candidates have been on the road campaigning nonstop for more than a year — and in some cases considerably longer than that.

The only way that Santorum and Gingrich, and Romney for the matter, force themselves out of a bed early every morning and hopscotch across the country in search of more — votes, money, attention — is to see the light at the end of the tunnel and to believe they can make it to that triumphant day when they seize victory.

But, as the thrill of the early votes wears off and the hard reality of the delegate math sets in, the bone-tiredness and frustration of a year (or more) of trying to unsuccessfully convince voters why you are the best choice begins to set in.

Take the 2008 Democratic presidential primary fight between then Sens. Hillary Clinton and Barack Obama. By the end of February, it became clear that Clinton had fallen hopelessly — or close to it — behind in the delegate chase.

And yet, she kept winning states — giving her and her campaign plenty of justification to stay in the race. (Sound familiar?) Then came an editorial board meeting with the Sioux Falls Argus-Leader (South Dakota) in late May in which Clinton said the following:

“My husband did not wrap up the nomination in 1992 until he won the California primary somewhere in the middle of June, right? We all remember Bobby Kennedy was assassinated in June in California. I don’t understand it.”

The Obama team immediately pounced, insisting that Clinton was invoking the assassination for political reasons. The New York Senator was forced to apologize. The whole episode left an unpleasant taste at the end of a campaign — the primary race formally ended on June 6 — that was, by any measure, one of the greatest in modern political history.

Why did it happen? Because Clinton was worn down. She was tired of having to answer question after question about why she hadn’t dropped out of the race yet. She was tired of trying to win an unwinnable race.

That’s the same mindset that seems to have infected Santorum and Gingrich in the wake of the Illinois primary and the endorsement of Romney by former Florida governor Jeb Bush .

Their windows of opportunity, which were always open a crack (at best), have now slammed shut. The danger for both men is that they linger in the race so long past the point which they should that they tarnish the (mostly) positive impressions they have left on the Republican electorate in the race. (Kind of like how Kareem Abdul-Jabbar just kept playing and playing — and playing.)

“Normally these are signs of a campaign on its last breath, but then again, given that Newt has been touring zoos, and Santorum is talking about how porn affects the brain, it feels like this final last gasp seems to never end,” said Todd Harris, an unaligned Republican media consultant.

We’ve reached the end of the end — or damn close to it — in the Republican race for president. The only question now is when (or if) Santorum and Gingrich recognize it.

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