Story highlights "I believe the majority of the Republicans in the US Senate are not going to vote for Donald Trump," McCaskill said.

"[A] great number of them will in fact vote for Hillary Clinton," McCaskill added.

(CNN) Democratic Sen. Claire McCaskill said in an interview Wednesday that she believes based on conversations she has had with her Senate colleagues that the majority of Republican senators will not vote for their party's presidential nominee Donald Trump, and that many of them will instead vote for Hillary Clinton.

McCaskill, a top Clinton surrogate, added that many Republican senators are publicly supporting Trump but privately they are supporting Clinton.

"I believe, and I'm basing this on some of the things my colleagues have said to me, I believe the majority of the Republicans in the US Senate are not going to vote for Donald Trump because they know that they can work with Hillary Clinton and get some things done," McCaskill told radio host McGraw Milhaven on Missouri's KTRS.

McCaskill reiterated her statement after Milhaven asked her to clarify. "I believe that a great number of them will not be voting for Donald Trump, and a great number of them will in fact vote for Hillary Clinton," McCaskill said.

McCaskill criticized Trump for his inability to get along well with others, and argued that Clinton had worked well across the aisle with Republicans during her time in the Senate.

Read More