Story highlights President Donald Trump has taken a sharp tone with Senate Republicans lately

Susan Collins was among three GOP senators to oppose an Obamacare repeal

(CNN) Sen. Susan Collins, a moderate Republican, said Monday that she was unsure whether President Donald Trump would be her party's nominee for president again in 2020.

Collins, speaking on MSNBC, also said she was uncertain whom she would back for president during the next election cycle. The Maine senator, who was one of three Republican senators to vote against a GOP-leadership-backed Obamacare repeal measure last month, noted that she wrote in House Speaker Paul Ryan for president last year.

"I didn't support the President when he was our party's nominee," Collins said. "That was a very difficult position for me to take. I'd never taken it before. Instead, I wrote in the name of Paul Ryan. And that was very hard for me to do, as a lifelong Republican."

Asked if she thought Trump would be the Republican Party nominee in 2020, Collins replied: "It's too difficult to say."

Trump has taken a sharp tone with Senate Republicans lately, blasting Senate Majority Leader Mitch McConnell for not successfully shepherding the Obamacare repeal measure. He has also taken to blasting his critics from the center and the right, including Collins and Sen. Jeff Flake, an Arizona Republican.

Read More