The GOP primary is so close in Michigan that it might not even be the Republican voters who decide who wins.
Today and yesterday, thousands of Democrats across the state have been called by automated political message services, urging them to vote for Rick Santorum in the primary as a way of prolonging the Republicans' nominating contest and battering Mitt Romney, the establishment's struggling candidate.
The "robo-calls" come from unlikely allies: Joe DiSano, a Democratic campaign consultant in Michigan; and Santorum's campaign, which sees the opportunity to become a front-runner in the race.
DiSano says that based off of a week's worth of robo-calls, 14,000 Democrats who committed to voting for Santorum will be called again today and reminded to vote for the right-wing, resurgent candidate whom President Obama would surely rather face than Romney.
"Hopefully of that 14,000, a good number of them turn out and make a difference today," DiSano said.
The Michigan Democratic Party hasn't endorsed DiSano's tactic, "but at the same time, no one has called yelling at me to stop," he said.
Mark Brewer, the state Democratic party chairman, told ABC News that "we don't encourage it" but that he expected "a few cross-over votes."
Not all state primaries have the same rules. In Michigan, voters can choose a candidate in either party's primary, regardless of their affiliation. They just have to ask for the ballot for the party for which they want to choose a candidate.
"There could be a million people who vote here today," Brewer said. "Fourteen thousand is a drop in the bucket."
But recent polls have put the race between Romney and Santorum about as close as it could be. Santorum holds a slight edge above Romney in many of them, but almost all of his leads are within the margins of error, categorizing the contest as a dead heat.
Remember how Santorum won the Iowa caucus by 34 votes? In a close race, 14,000 votes for Santorum might do it. That's why his campaign has been asking Democrats to vote for him in a pitch that argues their crossover selection would "send a loud message" to Romney.
Republicans tried the same crossover method in the 2008 Democratic primary as Hillary Clinton and Barack Obama jockeyed for the nomination. The firebrand radio host Rush Limbaugh branded himself the leader of "Operation Chaos," an effort to encourage Republicans to vote for Clinton to prolong the battle.
"They're allowed to vote," Santorum said of Democrats as reporters pressed him Monday night, as the robo-calls drew attention. "And anybody who wants to vote, I encourage them to vote. Why wouldn't we encourage people to vote for me?"
Robo-calls aren't the most effective way to motivate people to do something political, especially at the end of a long primary contest in which voters' phones have been jammed with the automated messages.
"They just don't work at all," said Michael Heaney, a University of Michigan politics professor. "Personal phone calls can be persuasive, but robo-calls are not likely to persuade people. Also, they're annoying."
Democrats say Romney's faltering is a sign that he's failed in a primary he was expected to dominate in the state in which he was born and went to high school, and of which his father was a popular governor.
Having shed the skin of a decided front-runner, Romney sharply criticized Santorum for reaching out to Democrats to sway the vote his way; Democratic operatives have been quick to point out that in 1992, Romney voted for Massachusetts Democrat Paul Tsongas in the presidential primary.
"I think he's already lost," Brewer said. "This should be a walkover today. ... He should win by at least 10 points. Anything less than that has got to be considered a loss."