Editor's Note: (Julian Zelizer is a professor of history and public affairs at Princeton University and a New America fellow. He is the author of "Jimmy Carter" and "The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society." The opinions expressed in this commentary are his. )
(CNN) What could possibly motivate a Republican to formally endorse Donald Trump and join his raucous brigade? With each primary and caucus victory, the pressure for prominent Republicans to take a stand on his candidacy greatly intensifies. But taking this step is not easy.
Announcing that you will back Donald Trump is to enter into an alliance with a person who is controversial, explosive and who can often get extremely nasty on the campaign trail.
This is someone who has repeatedly said things that offend women, Latinos and Muslims; who was slow to disavow white supremacist support and who has chosen to stoke, rather than calm, flareups of violence at his rallies.
This week, he predicted "riots" should he fail to be given the GOP nomination, even if he lacks the required delegate total. And even if a politician is willing to be associated with the incendiary things Trump has already said, it is impossible to know what he will do next, and that can be frightening for anyone in the political arena.
As New Jersey Gov. Chris Christie learned last week, you might even find yourself humiliated by Trump after you take the risky step of supporting and going out to campaign for him.
Thus far, Trump has received a few high-profile endorsements, including those of Christie, Sarah Palin, Sen. Jeff Sessions, Ben Carson, Jerry Falwell, and, at a much lower level, Florida Attorney General Pam Bondi. This is still a pretty limited list for someone as far ahead as Trump.
So why would any other Republicans decide to take this step? The question is becoming much more important with each week. As Trump closes in on the delegates that he needs to secure the nomination in this three-person race (though it is not clear he will reach the required majority), he will be pressing harder to secure more endorsements so that he can avoid a brokered convention in Cleveland.
Obtaining a job in a Trump administration will be a major motivating factor for many Republicans. As the possibility of a Trump presidency becomes more real, a larger number of Republicans will make the calculation that if they want to be part of his administration they will need to get off the fence sooner rather than later.
Trump is the kind of person who punishes anyone who stands in his way.
Those officials who come out in the next few weeks and play a role in helping him win some of the bigger states that loom ahead are hoping to be in a good position to be part of the White House should Trump manage to win the election.
Loyalty to party is a powerful force in our current era of polarized politics.
While the primary season is about deciding what kind of person you want to represent your party, the general election is about making sure that your party has power. Gradually the path forward for Trump's opponents is becoming less clear. If Trump demonstrates the potential to build a diverse electoral coalition that can defeat Hillary Clinton, this will be enough for some Republicans to line up behind him.
As Ben Carson explained when he announced his support, "I didn't see a path for Kasich, who I like,or for Rubio, who I like. As far as Cruz is concerned, I don't think he's gonna be able to draw independents and Democrats unless he has some kind of miraculous change."
These Republicans will separate their support for the campaign from the man.
Given that Hillary Clinton will be the Democratic candidate, the intense feelings that she elicits within the GOP will be enough to move some Republicans into Donald Trump's camp. There will be the moment, perhaps in the near future, when Republican turn their attention to the competition against the Democrats rather than among themselves.
If the anti-Trump coalition headed by Mitt Romney does not show any signs of strength, some Republicans may decide that it is time to heal the divisions in the party by accepting Trump to maximize their chances in the fall.
As Trump looks more and more like a winner in the party contest, there will be Republicans who actually like the candidate or at minimum are excited about what he can offer in the electoral arena who will finally step forward.
There might be a tipping point where this insurgency becomes legitimate, becoming less of a political circus than an actual competition. Once this happens, this will be a key moment for Trump to start securing a huge number of endorsements as more candidates are willing to stand up for a candidacy that once may have seemed too dangerous.
Nor will Republicans necessarily be worried about the risk of endorsing Trump only to have a brokered convention select a different candidate this summer.
If the nomination is decided at the convention, Cruz or Kasich -- or anyone else who enters the competition -- will need the support of everyone who backed Trump and have reason to court their vote.
The final factor that can move Republicans into the Trump camp will be animosity toward his opponents, particularly Ted Cruz. Though he is trying to position himself as the new "establishment" choice, Cruz has been as much, if not more, of an insurgent to the party than Trump.
He is also a politician who has personally burned many bridges with fellow party members in the Senate and the campaign. If Kasich no longer looks like a viable choice for a brokered convention, some Republicans might support Trump as a way to pay back their anger toward Cruz.
Taking the step of standing on the podium with Donald Trump will not be easy.
Every politician realizes the high costs that can come with this, particularly since the outcome of the fight might not be totally settled until the summer.
For many Republicans, this will come down to balancing political and self-interest with the difficulty of supporting a candidate who is genuinely distasteful to them and who risks bringing them embarrassment and anger from people they respect. But as Trump looks like the only real game in town, we'll see more Republicans deciding that this is a risk worth taking.
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