A Mitt Romney loss in Tuesday’s Michigan primary would have meant the effective end of his campaign. A John McCain win might have propelled the Arizona senator to the nomination. But Romney won handily, and now the race is as muddled as ever. There are at least three plausible contenders: Romney, McCain, and Mike Huckabee. If Rudy Giuliani wins the Florida primary later this month, we may even have a four-man contest going into Super Tuesday on February 5.

If you want to make your head spin, think back to the many different dynamics in the Republican race over the past year. At very the start of 2007, with no obvious conservative favorite, McCain was the frontrunner. He benefited enormously from George Allen’s implosion in the 2006 Virginia Senate race. (Some GOP pundits had previously been touting Allen as the next Ronald Reagan.) Then there was the fall of McCain—which coincided with last spring’s bitter debate over immigration—and the ascendance of Rudy Giuliani, who led in national polls for most of the year. After Giuliani vaulted to the front, many Republicans began searching for a more conservative alternative to the socially moderate New Yorker—a search which led to Fred Thompson’s candidacy. Along the way, Romney had attempted, with some success, to define himself as the conservative alternative to Giuliani. So when Thompson faltered, Romney’s prospects brightened. By the fall, there was a brief moment when the nomination looked to be his.

The former Massachusetts governor built his campaign on a momentum strategy. Romney excelled at raising money and could also draw on his own private fortune. He focused his money, attention, and organization on Iowa and New Hampshire. A Romney win in both of those states might have set up a Romney-Giuliani showdown, which Romney could have won. That scenario looked plausible in October and November.

But the rise of Huckabee scuttled Romney’s plan. The ex-Arkansas governor issued a strong appeal to evangelical Christians in Iowa, and wound up carrying the state by a wide margin. Losing Iowa damaged Romney in several ways. For one thing, it cast doubt on Romney’s claim that he alone could unite conservatives. For another thing, it aided the reemergence of McCain to top-tier status. After his loss in Iowa, Romney no longer seemed the inevitable New Hampshire winner. McCain had already been gaining ground in New Hampshire, and following the Iowa caucus he pulled away.

The Romney win in Michigan makes the Republican race a three-ring circus. A McCain loss in South Carolina and subsequent Giuliani win in Florida could add a fourth ring.

After all that, Romney simply had to carry Michigan—and preferably by a sizable margin. He grew up in the state, and his father once served as its governor. This gave him a certain “native son” appeal, and Romney won by a substantial 9 percentage points. It may have been predictable that he would dominate the Detroit metropolitan area, given his roots there. But Romney also championed the cause of middle-class Michiganders who are anxious about job losses in the auto industry.

This Saturday the GOP race moves to Nevada and South Carolina. It is extremely difficult to forecast Nevada because it is a low-turnout caucus that has never been held this early in the election cycle. Romney may be able to capitalize on the state’s relatively large Mormon vote—and perhaps on his work as president and CEO of the 2002 Winter Olympics in neighboring Utah—but a win in such a quirky contest would not necessarily signal that Romney can win elsewhere. To paraphrase the Las Vegas marketing campaign, the results of the Nevada caucus might just stay in Nevada.

Indeed, South Carolina and Florida are far more important than Nevada, and Romney does not appear poised to win, or even to finish second, in either of them. The South Carolina primary is shaping up as a battle between McCain and Huckabee. A McCain win would hurt Giuliani, since McCain takes independent and moderate voters away from the former New York City mayor. Giuliani has banked his hopes on winning the Florida primary in late January. But if McCain wins South Carolina, he will then have a good shot at winning Florida, where he and Giuliani are running close in the polls. McCain victories in those two states would give him a burst of momentum heading into Super Tuesday. He would then be the clear-cut frontrunner.

On the other hand, a Huckabee win in South Carolina would make the race even more chaotic. It would certainly bruise McCain and thus improve Giuliani’s chances in Florida. If Hizzoner carries the Sunshine State, we will be looking at a four-way race heading into the delegate-rich February 5 primaries. It is even possible that no candidate will win a majority of delegates before the Republican National Convention in early September.

The Romney win in Michigan makes the Republican race a three-ring circus. A McCain loss in South Carolina and subsequent Giuliani win in Florida would add a fourth ring. In that scenario, “circus” really would be an apt metaphor.

John C. Fortier is a research fellow at the American Enterprise Institute.