House Speaker Paul Ryan on Tuesday defended his endorsement of Donald Trump -- despite his frequent differences with the presumptive GOP nominee -- saying the only alternative is giving the presidency to Hillary Clinton.

"It is a binary choice," Ryan said at a CNN town hall hosted by Jake Tapper. "It is either Donald Trump or Hillary Clinton. You don't get a third option."

But the challenge facing Ryan was clear when he was asked a question by Zachary Marcone, a Republican who said he couldn't support Trump because he is "openly racist."

"Can you tell me, how can you morally justify your support for this kind of candidate?" Marcone asked.

Ryan didn't address the premise of the question, reiterating his stance that opposing Trump amounts to supporting Clinton. He pledged to always speak his mind when he disagrees with Trump but argued that the best chance for conservatives to have their priorities signed into law is with the businessman in the White House and pointed to the ability of the next president to nominate Supreme Court justices.

As he spoke of the next president's ability to choose Supreme Court nominees and influence the high court over the long term, Ryan criticized Ruth Bader Ginsburg. The 83-year-old justice is the subject of controversy after she told CNN this week that Trump is a "faker" who is driven by his ego.

"I think it is out of place in an appointed branch of government. That shows bias to me," Ryan said. "I don't think that is something she should have done."

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