If Rick Santorum can pull out a narrow victory in Tuesday’s Michigan primary, he might have Democrats to thank.

Or at least, that’s how the theory goes.

Republican presidential candidate and former Massachusetts governor Mitt Romney does an interview with the Motor Racing Network during his appearance at the NASCAR Sprint Cup Series 54th Daytona 500 race at the Daytona International Speedway in Daytona Beach, on Sunday. (REUTERS/Joe Skipper)

It even has a name: Operation Hilarity.

But the likelihood that they will actually tip the scales against Romney is pretty small, for a host of reasons.

This is actually a pretty familiar exercise in Michigan, where the state voted for Democrats George Wallace in 1972 and Jesse Jackson in 1988 thanks, the story goes, to Republicans crossing over. More recently, Democrats were credited with giving the state to John McCain over George W. Bush in the 2000 GOP presidential race.

The plot thickened in recent days, with both President Obama ’s campaign and a super PAC supporting Obama going up with TV ads in the state hitting Romney for opposing the auto bailout. In addition, the state Democratic Party sent an e-mail to supporters last week featuring video of a pair of Republican state senators urging Democrats to vote in the GOP primary.

The effort on behalf of Democrats isn’t a stated one, and both the Michigan Democratic Party and Obama’s campaign have plausible deniability that they are trying to undercut Romney (Obama’s team was careful to run an ad that also mentioned Romney’s GOP opponents were against the auto bailout, while featuring Romney more prominently; the super PAC focused only on Romney.)

“We’re not encouraging it, but it’s happened before and we expect it will happen again,” Michigan Democratic Party spokesman John Tramontana said of crossover voting.

But the seeds of a crossover operation have been planted in a way they weren’t in previous states, not to mention the fact that Michigan has a history of this kind of thing.

And Republicans say that, while crossover voting may not be an overwhelming factor, it is nonetheless a factor.

“Clearly, there are prominent Democrats and liberal activists trying to stir things up,” said former Michigan GOP chairman Saul Anuzis, a Romney supporter. “If the election is close, they could distort the results and give Santorum a false sense of success.”

Still, Anuzis said he expects the effect of this vote to be “minimal,” and other Romney supporters agree — a significant thing, given that crossover voting would be a great excuse for a Romney loss tomorrow.

“I suppose it’s possible,” said another Romney supporter, state Attorney General Bill Schuette. “I’m not stressed by it. I don’t lose sleep over it. What can you do?”

Anuzis noted that the 2000 effort was more overt, with Democrats wanting to send a signal to then-Gov. John Engler (R), who had supported Bush.

Similarly, it was clear in 1972 what was going on with crossover voters, said Michigan political expert Bill Ballenger.

“With George Wallace, you definitely had that happen. Republicans and independents flooded the primary and embarrassed the Democratic Party,” Ballenger said.

The 1988 election was more of a mixed bag. That year, the state was holding a caucus, which meant turnout was lower — which helped a lower-tier candidate like Jackson — and it was also harder for Republicans to infiltrate the process.

So how does this year compare?

Experts note that crossover voting must be viewed in a nuanced way, and that many, if not most, crossover voters are not mischievous members of another party trying to ruin the other party’s primary.

Just as often as someone crosses over to “raid” the other party’s primary, for example, they may also cross over for more wholesome reasons, such as simply wanting to take part in a competitive primary.

And if that happens in Michigan, it may actually help Romney, given he has much more appeal to liberals and moderates than does Santorum.

By contrast, in 2000, both so-called “raiders” — those deliberately voting for McCain to thwart Engler and Bush — and Democrats who were voting for their actual preferred candidate likely voted for McCain over Bush.

“The stronger motive was that McCain was just a more moderate candidate,” Ballenger said.

Similarly, studies on crossover voting show the effect of these “raiders” is rather small.

In 1988, with the GOP nomination sewn up early, Michigan wasn’t the only state where some Republicans crossed over to vote in the more competitive Democratic primary.

A study of crossover voting on Super Tuesday in 1988 showed that more than 10 percent of voters in the GOP primary were Democrats. But of that group, only about one in eight were “raiders,” while well more than half were either voting for their actual first choice in the general election or simply their first choice in the Democratic primary.

So overall, less than 2 percent of voters were coming from the other party simply to cause mischief.

That doesn’t mean the number will be that low in Michigan this year. Indeed, with so much focus on the possibility of crossover votes, Democrats may be more likely to turn out and vote Republican.

And if the race is as close as some polls indicate, it may be enough for Santorum to pull the upset.

But a lot of things have to fall into place in order for that to be the case, and it’s not likely to tip the scales.