Calling 2016 the "year of the outsider," former Vice President Dan Quayle told CNBC on Thursday that Donald Trump can beat Hillary Clinton.

"He knows how to win," Quayle, who's backing Trump, said in a "Squawk Box" interview. "He knocked off 16 Republican and a lot of them were really good, solid people and would have been good presidents."

Trump arrived at GOP headquarters in Washington on Thursday to meet with House Speaker Paul Ryan, who said last week he's "not ready" to support the businessman-turned-presumptive-GOP-presidential nominee. The two hope to open a dialogue aimed at unifying the Republican Party.

Quayle, vice president under George H.W. Bush, said he "not going to get into Paul Ryan's head," but believes the speaker was buying time with those comments because Texas Sen. Ted Cruz folded so quickly after Indiana.

"[Trump] is going to find out as he starts to go around Capitol Hill, folks in Congress, they need a lot of stroking. You got to be nice. He can be nice when people are nice to him," Quayle said.

Quayle said Trump, if elected president, will have to deal with Ryan.

"In business, you try to get a deal, it doesn't work out; guess what, you just go onto the next deal," Quayle said. "In this situation as you're president, if you don't get a deal, you go on to the next deal but you're dealing with the same people."

Quayle predicted Ryan will come around because "a great majority of his caucus will support Donald Trump, without qualification."

The obvious choices for Trump's running mate would be former GOP presidential rivals Sen. Marco Rubio of Florida or Ohio Gov. John Kasich, Quayle said.

"But the one I think would be a really good choice, not on too many people's lists is ... Rob Portman," the Republican senator from Ohio, Quayle said. "Look at his background — congressman, trade representative, OMB director, U.S. senator — he's got it all."