Michigan primary: For Romney, a must-win Mitt Romney faces what is arguably his first must-win primary of the 2012 campaign in Michigan today, the start of an eight-day stretch that will determine whether Republicans begin to close ranks around a more moderate frontrunner, rally behind avowed conservative Rick Santorum -- or scramble for a new alternative to face President Obama in November. A combined 59 delegates are at stake in Michigan and Arizona today, the last two primaries before the playing field expands dramatically a week from today on Super Tuesday, when states with more than 400 delegates will hold votes. According to an updated tally from the Republican National Committee, Romney has the delegate lead in the GOP race -- 73 to 29 over Newt Gingrich. Rick Santorum and Ron Paul lag behind in single digits; only a handful of convention votes are bound this stage. Arizona appears to be the safer bet for Romney as voters go to the polls. The RealClearPolitics average of public polling has him leading Santorum by more than a dozen points. The real focus of the past two weeks has been Michigan, which on paper should have been a lock for Romney. He was born in Detroit and grew up in the suburbs, his father was a three-term governor, and Romney carried the state during his 2008 presidential run. Between his own campaign and a "super PAC" run by his allies, he's again outspent the field. But polls show the race is a dead heat there between Romney and Santorum, the former Pennsylvania senator who of late has had success in appealing to more conservative GOP voters who remain distrustful of Romney. Because Michigan apportions its delegates on a district-by-district basis, with only two of the 30 based on the statewide vote, the real prize is the momentum an outright victory would bring to either candidate. Momentum has proved to be fleeting in the GOP contest so far. Romney seemed to have it after what was initially declared a razor-thin win in Iowa, followed by a more substantial triumph in New Hampshire. But updated totals a few weeks after the Iowa vote showed that Santorum had in fact edged Romney there, and Gingrich followed with a strong victory in South Carolina. Romney again rebounded with back-to-back victories in Florida -- where his organizational and financial advantage proved insurmountable -- and Nevada, only to have Santorum pull off a stunning trifecta in contests in Colorado, Minnesota and Missouri. Now, more than at any point thus far, Romney faces the real possibility that a loss would erase whatever is left of the inevitability that had been driving his candidacy. It would undermine him heading into Super Tuesday, raising the specter of a nominating race that would not produce a candidate with a clear delegate advantage before the party's August convention. Many Republicans are worried that a Santorum ticket would be too conservative to defeat Obama. But if Romney wins today, it would go a long way toward convincing Republicans -- especially some of Romney's own backers -- that he is likely to be the nominee and end talk of finding a new candidate to jump in. "I'm ready for it to be over tomorrow," Virginia Gov. Bob McDonnell said this weekend. If [Romney] wins Arizona, wins Michigan, has a good Super Tuesday - I think there's a path for it being over or close to over. One potential wild card in Michigan: the state allows Democratic voters to cast a ballot in the Republican primary. There has been chatter about Obama supporters pushing for a Santorum vote, well aware of the damage it would do to Romney and the GOP by extending the fight. The polls close in Michigan at 8 p.m. local time. Arizona's polls close at 7 p.m. local time. Later this week, Washington state Republicans will hold caucuses. Super Tuesday comes next, with 10 states voting: Alaska district conventions (27 delegates) Georgia primary (76 delegates) Idaho caucuses (32 delegates) Massachusetts primary (41 delegates) North Dakota caucuses (28 delegates) Ohio primary (66 delegates) Oklahoma primary (43 delegates) Tennessee primary (58 delegates) Vermont primary (17 delegates) Virginia primary (49 delegates) Wyoming caucuses (29 delegates, held through March 10)