Why Dick Cheney isn't backing Donald Trump

The former vice president has declined to endorse Donald Trump – or any other candidate for the Republican presidential nomination.

They are perhaps two of the most divisive figures in the Republican Party. So what do Dick Cheney and Donald Trump think of each other? Not much, it appears.

In interviews for his new book, former Vice President Cheney has declined to endorse the billionaire businessman – or any other Republican candidate.

"I don't know the man, I've never met him." Cheney told CNN. "I don't want to be in the business of rating candidates at this point or grading them."

But while he's tried to remain tight-lipped about his thoughts on Mr. Trump, he did react to the unlikely candidate's success in the polls.

"I've been surprised that he's done as well as he has. I think most of us have on the Republican side," he added.

Cheney has been making the media rounds with daughter Liz for their new book out Tuesday, "Exceptional: Why the World Needs a Powerful America." In it, Dick and Liz Cheney make a case for a more assertive US foreign policy, weighing in on the Iran nuclear deal (which Cheney calls "tragically reminiscent" of the Munich pact), the Iraq war, and President Barack Obama ("worst president we've ever had").

On the interview circuit, they have shared their thoughts on the 2016 race so far. Liz Cheney said Trump appealed to voters frustrated with Washington and its leaders.

"He is obviously touching a nerve," she told CBS This Morning. "People are reacting to the straight talk, they're reacting to the sense of the need for America to stand tall again.... You're seeing the resonance of that particular message [in Trump]."

And while Mr. Cheney emphasized that he and Liz are "religiously staying away from evaluating candidates at this point," he did offer praise for two candidates – one from each side of the aisle.

"Jeb's a good man; I thought he was a good governor of Florida," Cheney told USA Today. But he declined to endorse former Florida Gov. Jeb Bush and said, "He's got to go out and earn it, the same as anybody else does."

The surprise? Cheney appears to be a fan of Vice President Joe Biden.

"I'd love to see Joe get in the race," Cheney told CNN. " 'Go for it, Joe.' He's tried twice before; he obviously is interested. I think there's a lot of support for him in the Democratic Party. I think it would stir things up. They're short candidates on their side, so I'd urge Joe to have a shot at it."

In all likelihood, Trump, who, like Cheney, opposes the Iran nuclear agreement, won't hesitate to share his thoughts on George W. Bush's vice president.

He certainly wasn't shy in 2011, when he said in a video posted to YouTube that Cheney, who had just released a memoir, "In My Time," about his years in the Bush White House, had done "a rotten job as vice president."

"I didn't like Cheney when he was a vice president, I don't like him now, and I don't like people that rat out everybody, like he's doing in the book."