On the list of campaign shockers, this one is pretty low. Sen. Bob Corker (R-Tenn.), a well-respected foreign policy leader in the Senate, told our own Bob Costa he's taking himself out of consideration for Donald Trump's vice presidential pick.

"It’s just not the right thing for me," Corker told Costa. "And I don’t think it’s the right thing for them.”

To say these two politicians are very different people is like saying the Kardashians are maybe a . Corker is a behind-the-scenes policy-oriented deal maker, not one to make headlines with splashy insults. Trump is -- well, Trump is Trump. The two took their mismatched relationship for a test drive Tuesday, and the cracks were already pretty obvious.

UPDATE: Trump's campaign is disputing Corker's own words, telling reporters the senator is still in contention. They may still be considering him -- but in Corker's comments earlier, he didn't appear to be returning the favor. Here's what Corker told the Post's Robert Costa:

It’s a highly political job, and that’s not who I am,” Corker said. “We had a very open conversation about that, and actually, we have been very candid about it from the very beginning of our meetings. I left there feeling very good about him as a person but also realized that at age 63, I know the things I’m good at doing. And knowing what a candidate for vice president has to do, it’s just not the right thing for me, and I don’t think it’s the right thing for them.”
“So, I’m going to move on,” Corker said. “I am very positive about him as a person. It was incredible to be with him in Raleigh and see the way people react to him. They’re so excited, and I truly believe he has such an opportunity ahead."

We'll update this as needed.

But the confusion about whether Corker's in or out doesn't change the fact Corker was never going to be Trump's vice president. Here's why:

—We're not really sure how Corker's name got into the mix in the first place.

If you asked us to draw a list of Trump's vice presidential picks from scratch, Corker wouldn't be on it.

Oh wait, we did draw up a list of potential veep picks soon after Trump clinched the GOP nomination. And Corker was nowhere on Fix founder Chris Cillizza's list. (No. 1 was Chris Christie, a pugnacious politician who's a much more obvious match with Trump in terms of temperament and style. He's still on our list for a likely veep pick.)

The best we can tell, Corker's name got thrown into the mix after he praised -- nay, "gushed," according to Politico -- a foreign policy speech Trump gave in April.

"If you look at the broadness, the vision, I thought it was a major step forward," Corker said on MSNBC after the April speech.

Corker's words carry a lot of weight in the foreign policy world, given he's the chair of the Senate's Foreign Relations Committee. All of a sudden he was meeting with Trump at Trump Tower and being vetted for Trump's veep pick.

—Read between the lines, and Corker was still hesitant about Trump

But Corker's praise of Trump's foreign policy came with conditions. He seemed to say it was better than he expected -- not necessarily synonymous with a great speech. And in a statement after Trump spoke, he urged Trump to share more details.

"My sense is that he will evolve," Corker told reporters after meeting Trump for the first time in Trump Tower in May.

Over the next few weeks, Corker briefly advised Trump on foreign policy and had nothing good to say about it. He told The New York Times's Jennifer Steinhauer in June he was "discouraged by the results," adding "I don’t know that I really have a lot to say."

—The two don't see eye to eye

Especially when it comes to foreign policy. And that's a notable division given Corker's foreign policy gravitas would have been his biggest gifts to the Trump ticket.

As Roll Call's David Hawkings points out, Corker supports free trade deals like the Trans-Pacific Partnership that Obama's trying to get through Congress. Trump eviscerated that and other trade deals in a recent speech, calling the pact "the death blow" for manufacturing in our country.

Corker helped write the 2013 immigration bill the Senate passed (he worked on a provision boosting border security). Trump has suggested deporting immigrants in the country illegally and banning others from coming in.

Trump is quick to call legislation that contains a path to citizenship "amnesty." Corker hates that word.

"I get really frustrated with people on my side of the aisle who say that anything you do on immigration is amnesty," Corker said a few years ago.

And Corker has focused on nuclear non-proliferation while Trump has suggested more countries should have nuclear weapons.

—Corker's not an attack dog

The two don't match up on style, either. Think quick: When's the last time you read a headline about Corker saying something splashy that didn't have to do with Donald Trump?

We can't recall one either. And that's because Corker just isn't the kind of politician who's attracted to controversy.

No need to take our word for it. Again, Corker told Costa as much in explaining why he didn't want to be Trump's veep.

"It’s a highly political job and that’s not who I am," he said.

He knows full well it's a role that is going to require jumping in the gutter in what's shaping up to be one of the nastiest general elections in recent history. And Corker's just not down with that.

He blew his tryout

Trump has been taking his veep picks on public tryouts of sorts. Tuesday night was Corker's turn at a rally in North Carolina.

But when Trump thrust Corker in front of the microphone, Corker seemed literally speechless.

"I wasn't going to say anything," Corker said. "I just came to visit."

"He sounded like he didn't know quite what to do," wrote Roll Call's Niels Lesniewski.

Other journalists noticed the awkward-ness, too:

Less than a day later, Corker publicly took himself out of the running.