A GOP senator had a tense exchange with the 'Morning Joe' co-hosts when they asked about Trump

Republican Sen. Bob Corker had an awkward exchange with the co-hosts of MSNBC's "Morning Joe" on Wednesday when they asked him to defend his party's presidential nominee, Donald Trump.

Corker, the chairman of the Senate Foreign Relations Committee, went on the show to talk about Iran. The situation became somewhat tense when co-host Mika Brzezinski asked Corker why he thought Trump would make a better commander-in-chief than Democratic presidential nominee Hillary Clinton.

"I didn't come on the program to talk about politics," Corker said. "I think that, you know, you asked me to come on to talk about public policy. I will say, in general, look, the foreign-policy establishment does need a shake-up."

He continued, saying mistakes have been made on both sides of the aisle that have created "a lot of instability around the world." He also mentioned the generals and admirals who came out Tuesday in support of Trump.

At times Corker kept with Trump's message, saying the US is "not respected around the world today." But at other points, he diverged from it, saying America has "retreated too far" from the rest of the world. Trump often espouses a message of "America first," which some foreign-policy experts view as isolationist.

Co-host Willie Geist asked Corker about Trump's stated plan, should he win the presidency, to give generals 30 days to come up with a plan to defeat the terrorist group ISIS.

Corker said he hasn't had discussions with Trump or Clinton about their strategies to defeat ISIS. But Geist pressed Corker, asking if he agrees with the general idea of Trump waiting until he takes office to figure out a plan for defeating the group.

"I haven't heard either candidate be very crisp as it relates to dealing with ISIS," Corker said. "... Again, I know that because I'm a Republican and I'm here in front of you, you want to slant this in a particular direction, but I think in general, and I don't mean that to be offensive, but in general, I haven't heard a lot of crispness as it relates to the policies that really affect our nation from anyone."

Geist responded: "Well, chairman, that's why I'm asking you. Donald Trump is the candidate that you're supporting. That's why I'm asking you about him. Does it concern you as the chairman of [the Senate Foreign Relations Committee] that you don't quite know what he would do as the commander-in-chief about ISIS?"

Corker pivoted to put the focus on President Barack Obama.

"Well, it concerns me that we've got another four or five months under an existing president that does have the input of lots of people, and has had for seven and a half years, and that we've allowed Syria to devolve into the greatest humanitarian crisis of modern times. We still have no plan."

Geist and Brzezinski again asked about whether Corker is confident Trump would do better than the current administration.

"I think certainly we've got some debates that are coming up. My guess is that intelligent people like all of you on this broadcast will be asking those questions, and my guess is those kinds of things will be illuminated over time. And they're spending time, each of them, trying to figure out how more crisply they can lay out their plans. That's what a campaign does, that's how it evolves, and I look forward to that when it happens."

Brzezinski looked puzzled and noted: "It seems like you don't feel comfortable talking about Donald Trump."

Corker again declined to specify his views on Trump, saying: "Well, I don't feel comfortable coming on a program and being sort of a judger of the two."

He said he's focused on his job as chairman of the Senate Foreign Relations Committee.

"You guys wake up each day and you're focused on who shot John and the political give-and-take," he said.

Brzezinski cut in.

"Then how about an easier - do you have confidence in Donald Trump as commander-in-chief, especially as it pertains to foreign policy?" she asked. "I'll make it really broad and easy."

Corker dodged the question.

"Again, look, neither of the campaigns to my knowledge have laid out much anything that is specific relative to getting people back to work, growing our economy, dealing with the entitlement programs," he said. "I think the appropriate response for all of us is to when these debates occur and people have to tease out these very specific issues, hopefully, hopefully moderators are going to push that, then we can judge."

Brzezinski told Corker that he wasn't answering her question.

"Donald Trump is deepening in what he's throwing out. He's shaking up the foreign-policy establishment, and I think we're going to have a much clearer sense of where he is as he moves ahead," Corker said. "But look, Mika, I've got a job to do here, and it's not to be the referee on a presidential campaign."

Watch the full clip below: