It boils down to simple addition. In order to clinch the nomination, a candidate needs to secure more than half of the party’s delegates. In primaries past, a presidential hopeful who dominated Super Tuesday could come close enough to that 51 percent mark that he would be considered the presumptive nominee. (Think of John Kerry in 2004 and John McCain in 2008.) But this time around, the number of delegates available early on will significantly shrink, making it impossible for someone like Mitt Romney to take out his primary rivals in one fell swoop…

That spells trouble for Romney, who currently is leading most national polls but stands to lose steam the longer the race is drawn out. At the same time, it could create an opportunity for late entries like Sarah Palin or Texas Gov. Rick Perry—especially since this cycle’s scaled-back Super Tuesday will include several Southern states, where Romney’s moderate record and Mormon faith don’t play well.

If Romney fails to earn “presumptive nominee” status in March by losing Super Tuesday states like Texas, Oklahoma, and Tennessee, he’s probably not going to call it quits then and there. More likely, he will rely on his well-stocked campaign war chest to hold on until later blue-state primaries where he’s expected to perform better, like New York (April 24) and California (June 5). In other words, get ready for one long, drawn-out horse race.