Jeb Bush suspended his campaign for president on Feb. 20. The Fix's Chris Cillizza breaks down why he was never going to be president. (Video: Peter Stevenson/The Washington Post)

The only way that Donald Trump will not win the GOP nomination, it seems, is if the voters who support Marco Rubio, Jeb Bush and John Kasich rally around Kasich or Rubio moving forward.

This isn't foolproof: Adding up Rubio, Bush and Kasich in national polling, for example, totals 30 percent, to Trump's 34 percent. But in South Carolina it would have dropped Trump to second place, which is about as good as the Republican establishment could hope for.

With Jeb Bush now out of the race and Ben Carson out of the race in the eyes of literally every person paying attention to the presidential race, save Ben Carson (if he's even paying attention), it's worth wondering where their supporters might go. The thinking is that all those Bush supporters will go to a Rubio or Kasich, for example, but is that true?

It's hard to say. The problem is that supporters of Bush and Carson are so few that polling on where they'll go next is necessarily a tiny sample size. In a recent USA Today/Suffolk University poll, only 20 people said they planned to back Bush and only 13 signed up for Carson. That's the problem, right? They have little support, so they have to drop out.

Here's where those 33 people would go. This is not representative! But it reinforces that the idea that all of the vote will go to opponents of Trump is flawed.

We noted earlier this week that Trump was leading among somewhat conservative and moderate Republicans -- the people that were supposed to be backing the Bush/Rubio/Kasich types.

In South Carolina, Trump won a plurality of moderates, too -- and it's not clear that the 9 percent of that vote backing Bush will all fall in line behind Rubio or Kasich. According to that Suffolk/USA Today poll, 15 percent of Bush backers went to Trump! That's only three people, mind you, but it is not zero.

As we noted earlier this week, a race that narrows to just Trump vs. Rubio or just Trump vs. Ted Cruz is a race that Trump probably loses. But that requires Kasich and Carson and Rubio or Cruz getting out. March 15 is the Ohio primary and the Florida primary, which both Kasich and Rubio will want to hang around for -- making it even less likely that Trump will suddenly start trailing a consolidated centrist candidate.

Making it even more likely that he'll be the nominee.