Republican National Committee chairman Reince Priebus. (Susan Walsh/AP)

This weekend, the head of the Republican Party suggested that he might punish the fellow 2016 presidential candidates who don't support Donald Trump, possibly by making it harder — or even impossible — for them to run for president down the line.

That's a pretty unusual thing for a party leader to say, but it’s not clear how the Republican Party could carry out this threat without changing Republicans' nominating process in equally unusual ways.

Here's what Republican National Committee Chair Reince Priebus said Sunday on CBS's "Face the Nation" about former presidential candidates Jeb Bush, John Kasich and Ted Cruz, none of whom have endorsed Donald Trump despite signing a pledge to support him: "Those people need to get on board. And if they're thinking they're going to run again someday, you know, I think that we're going to evaluate the process of the nomination process, and I don't think it's going to be that easy for them."

Priebus's threat was met with wide skepticism from other party leaders, including Ohio Gov. John Kasich, who has said he probably is not supporting Trump and whose top adviser put out a letter Sunday bashing Priebus.

Priebus's argument appears to boil down to a few specific threats; threats that we can, with the help of Robert David Johnson, a history professor at Brooklyn College, follow to fruition to their sometimes-confusing, often-surprising results:

Threat No. 1: "People who agreed to support the nominee, that took part in our process, they used tools from the RNC."

Priebus seems to saying that these candidates ran their campaigns with the help of the RNC, so now they need to help the RNC elect the candidate for president.

The Republican National Committee has spent a lot of money creating valuable databases of likely Republican voters throughout the country. Typically, the RNC shares that information with Republican candidates for president (for a price), like it did all of the 2016 candidates.

How that threat might manifest itself: Totally and completely unclear. Sure, it would be within Priebus's power, if he's in charge, to block access to valuable voter information. That would just be ... a messy activity. "As party chair you'd be forced to determine, 'Did Candidate X do enough to justify being on the ballot four years down the road?' '' Johnson said. "And it would be a crazy process."

Of course, all this is dependent on the mood of the party — and who's in charge of it come 2020.

Threat No. 2: "In order to be on the ballot in South Carolina, you actually have to pledge your support to the nominee, no matter who that person is. What’s the penalty for that?"

In the very next sentence, Priebus said this "wasn't a threat." But it sure sounds like Priebus is raising the specter of not helping candidates navigate ballot legalese to get on the ballot in time for a state's nominating process. (Every state can make its own rules, and with 50 states, it gets complicated.)

How that might manifest itself: We guess the RNC could just not help certain candidates when they ask for help on the ballot. But generally, the RNC's legwork is done well before the primary. The committee works with state Republican parties to make sure everyone understands everyone else's ballot rules. Plus, the candidates themselves often hire lawyers to make sure they comply.

Threat No. 3: "And if they're thinking they're going to run again someday, you know, I think that we're going to evaluate the process of the nomination process, and I don't think it's going to be that easy for them."

This could be interpreted a number of ways, but one possibility is that Priebus is suggesting that the party reorder what states vote first in the Republican primary process, perhaps to move states that favor non-Trump-supporting candidates to the back of the process.

How the threat might manifest itself: The party was already considering stripping Nevada of its early vote status (for three presidential elections, it's been in the top four alongside Iowa, New Hampshire and South Carolina). But that debate has less to do with the candidates Nevada favors and more to do with the trouble Nevada Republicans have had holding a high-profile nominating vote. Still, Priebus could seize on this debate to reorder the primary schedule in drastic ways.

Threat No. 4: CBS's John Dickerson asked Priebus: "[W]ould the party itself penalize somebody who does not make good on the pledge that they made to support the party's nominee?"

Priebus replied: "I think these are things that our party's going to look at in the process."

How the threat might manifest itself: Again, no idea. When the candidates took the pledge, it was nearly universally viewed by Republicans as a political symbol of unity, not legally binding document. (The fact that months later Trump publicly toyed with the idea of abandoning it highlighted the lack of enforcement options.) But that doesn't mean it can't be politically binding: Priebus could simply make his own rules and tell Bush, Cruz and Kasich — all 2016 candidates who haven't explicitly said they support Trump: You violated your pledge. You're out of GOP presidential politics.