Mitt Romney is facing "a day of reckoning" as the Republican Party holds its primaries in Michigan and Arizona on Tuesday. With Romney and Rick Santorum neck and neck in Michigan, Romney is making an eleventh-hour push to stave off what would be a humiliating defeat in his home state. In Arizona, a state with a disproportionate number of Romney's fellow Mormons, Mitt went into the vote with a commanding double-digit lead in the polls. What will tonight's results say about the race for the GOP presidential nomination? Here, five points to consider:

1. A loss in Michigan could cripple Romney
Michigan — the state where Romney was raised, and where his father was a popular governor — "is arguably his first must-win primary of the 2012 campaign," says Michael A. Memoli in the Los Angeles Times. On paper, Michigan "should have been a lock for Romney," but he faltered when the party's more conservative voters flocked to Santorum. A win would "go a long way toward convincing Republicans" that Romney would make a strong nominee. "A loss would erase whatever is left of the inevitability that had been driving his candidacy."

2. And Santorum might win even if he loses
Santorum's big lead over Romney vanished after a poor Arizona debate performance "and a string of conservative remarks on cultural issues that have called into doubt his viability in a general election," says Peter Hamby at CNN. But in the end, says Santorum adviser John Brabender, by giving Romney a run for his money in his home state, "we have already won." That's only partly true, says Robert Stacy McCain at The American Spectator. Coming close might be a "symbolic victory," but "an actual upset win for Santorum would be a major breakthrough for the 2012 campaign's longtime underdog."

3. Democratic mischief could decide the race
If Santorum wins, "he might have Democrats to thank," says Aaron Blake at The Washington Post. Michigan allows Democrats to cast ballots in the GOP contest, and Daily Kos founder Markos Moulitsas is urging Democrats and independents to vote for Santorum — the effort is called "Operation Hilarity" — to help President Obama by weakening likely nominee Romney and prolonging a damaging GOP primary fight. Even Santorum put out a robocall urging Democrats to back him, says Ed Morrissey at Hot Air. Now, Democrats say they have 12,000 Michiganders ready to back Santorum. "If a few dozen votes could decide Iowa, why couldn’t a few thousand decide Michigan?"

4. After Michigan, all eyes will turn to Super Tuesday
The votes in Michigan and Arizona won't definitively settle anything, says Jim Malone at Voice of America. But they're important because they "set up the Super Tuesday primaries and caucuses on March 6," when a whopping 400 delegates are up for grabs. Every candidate wants to go into that crucial 11-contest day with the wind at their backs. Tuesday's results will determine who scores that critical momentum.

5. No matter what, the GOP will still dream of a white knight
If Santorum wins Michigan, "the panic already gripping the Republican Party will deepen," says Frank Bruni in The New York Times. But even if Romney cleans up in Arizona and Michigan, he'll still be dogged by the sense that he only won thanks to a home-team advantage, not "the sheer hubba-hubba of his appeal." You can bet that regardless of who wins tonight, Republicans will go to sleep plagued by the same old angst, and dream of a white knight — Mitch Daniels? Jeb Bush? — who will come to their rescue.