Many attribute the rise of Donald Trump in the Republican presidential race, along with the popularity of Ted Cruz, to the continued prominence of the tea party movement within the GOP. While that’s certainly part of the story, it’s not the entire tale. The success of Trump and Cruz is not just due to their winning over more conservative voters, it’s also thanks to the centrist wing of the Republican Party being more divided than ever before.

Donald Trump addresses a crowd in Aiken, South Carolina, on Saturday. Christopher Aluka Berry | Reuters

While Cruz and Trump are dominating the more conservative Republican voters, a wide variety of options confront centrist Republicans: Marco Rubio, Jeb Bush, Chris Christie, John Kasich, and Carly Fiorina could all be considered more traditional, establishment candidates. Rubio is clearly leading this group, but is far from the overwhelming favorite, allowing the others the opening to remain in the race.

In Iowa, these candidates collectively take up 23 percent of the vote, according to the latest poll. That alone wouldn’t be enough to win, but it would certainly put that theoretical candidate in the conversation with the other top-tier candidates, and on the day of the caucuses he might be able to pull off the victory. Of course, winning Iowa is no guarantee to win the nomination: a candidate has often won the Iowa caucuses and gone on to falter down the stretch.

However, in New Hampshire it’s a different story. There, Trump is leading by 15 points in the most recent poll — but that’s only with 27 percent. In the Granite State, the establishment rift is even more evident: those five candidates are splitting up 41 percent of the vote, which would easily best Trump. Unfortunately, there is no clear leader among the establishment candidates in New Hampshire. Chris Christie, who gets 2 percent in Iowa, is polling at 12 percent, which puts him ahead of Rubio. Bush and Kasich aren’t far behind, either, giving them reason to be hopeful.

This could change following the Iowa caucuses, of course. If Rubio does better than expected in the caucuses, that could significantly improve his standing in New Hampshire. Then he might begin to draw support from more New Hampshire Republicans who don’t want to see Cruz or Trump win the nomination. That might give him the chance to pull off an upset win in the New Hampshire primary or at least a strong second-place finish.

If the field remains muddled, that gives Trump and/or Cruz a significant advantage going forward. They are already in a strong position, and will be in an even stronger one if Ben Carson continues to fade, as they’re likely to garner much of his support. The question, though, is not just if certain candidates will drop out, but when.

It is beginning to be time for some of these candidates to make tough decisions. They should consider carefully how much a second or third-place finish in New Hampshire will really help revive their campaigns if they finish closer to the rest of the field than to the winner of the primary. If the current polls are accurate and there’s no dramatic shift, the GOP could be in for a long, costly, and damaging nomination process that might last all the way to the floor of the 2016 convention.

Trump has risen to the forefront by preying on people’s fears, but he’s also helped by a large, fragmented field. In a race with fewer candidates, he likely wouldn’t be getting much more support than he is now. It’s certainly still possible to stop Trump from winning the nomination, but that would be an easier task for voters if fewer people were running and the choices were more clear.