Republican National Committee Chairman Reince Priebus. (Brian Snyder/Reuters)

It's easy to bash Reince Priebus.

How could he, as chairman of the Republican National Committee, let Donald Trump become the Republican nominee!? And, once Trump won, how could Priebus throw his lot behind the real estate billionaire and act as a surrogate for him?!

Here's the thing: There's almost nothing Priebus could have done — or should have done — to "stop" Trump. And, now that Trump is the party's candidate, it is literally Priebus's job to stand in defense of him.

Let's tackle the first critique first — that Priebus should have kept the Republican nomination from Trump.

How, exactly, would you envision Priebus doing that? There were 17 candidates in the Republican race. There was every reason to think someone other than Trump would be the candidate. And, every time Trump opened his mouth, it seemed he was on the verge of dooming whatever slim chance he had at winning — or even being a serious contender.

Once it became clear Trump was in it for the long haul — and, to be clear, no one saw that coming — the only possible route to beating Trump was to consolidate the anti-Trump vote behind one candidate. To do that, you needed a slew of the more establishment politicians to not only get out of the race but also decide to endorse the presumed strongest Trump alternative. Anyone who has spent five minutes around politics and politicians knows how impossible that task is. Everyone agreed that the field needed to be trimmed. No one agreed that they should be the person to step aside for the good of the party.

No chairman — not even Haley Barbour, widely regarded as the archetypal RNC chair — has the ability to end presidential campaigns if the candidates themselves don't want them to end.

Then there is the fact that Republican voters wanted Trump to be their candidate. As I wrote way back in the spring, it was clear that whether or not nominating Trump was a good thing for the party, it was clearly the will of the GOP base. He won more than 13 million votes — a total, as Trump likes to remind everyone, that was the most in the history of the Republican primary.

Stopping Trump by extraordinary means would have meant, quite literally, subverting the will of the Republican Party. And, Priebus, as chairman of the Republican Party, simply couldn't — and shouldn't — do that. And, if he did, there's a very real possibility that he would have been deposed as chairman. And that he should have been.

(Side note: Denying Trump the nomination by "ordinary" means was impossible given the real estate mogul's outsider campaign and his willingness to largely fund his own campaign. Denying Trump endorsement or fundraising help actually made him stronger, not weaker.)

Now, for the criticism that Priebus should have walked away from Trump once it became clear the controversial developer was going to be the nominee.

Why? And how?

Again, Priebus is the chairman of the Republican National Committee. He is elected to that job by 168 committeemen and committeewomen who are, theoretically, meant to represent the broader Republican Party. He is the face of the organization but, in truth, almost all of the power lies with those 168 people. And those 168 people don't like official Washington all that much and have long been fed up with how the establishment tells them things should be. Priebus has succeeded as chairman — he is currently in his third term in the job — because he has always understood that his only constituency, really, is those 168 people. (Priebus is like NFL Commissioner Roger Goodell in that way.)

It really isn't Priebus's job then to decide whether Trump should be the nominee — or whether the party as a whole should "walk away" from him. His job is to do everything he can to elect the person that the party chose. And that person is Trump. Period.

If you look closely, it's clear that Trump is not Priebus's cup of tea — but that he is committed to doing his best by the party.

Check out Priebus's interview with "Meet the Press" moderator Chuck Todd on Sunday. "I just don't speak for Donald Trump," Priebus said at one point. "I mean, those are the things that Donald Trump is going to answer," Priebus said at another. Then there's this:

CHUCK TODD: Let me ask you about birthright citizenship. It's still on Donald Trump's website. Is he going to call for the end of birthright citizenship?

REINCE PRIEBUS: You're going to have to ask him.

It's very clear what Priebus is saying without saying it: I am the chair of the Republican Party. Donald Trump is the nominee of the Republican Party. That means I am going to do what I can to get him elected. But I am not going to try to explain all of his policy views or defend them.

Priebus doesn't have the luxury — which lots of Republican consultants questioning him from the sidelines do — to simply throw up his hands and walk away from Trump. He has to stand and fight for the party's controversial candidate. That's the job. And that's what he's doing.