After saying she has not focused on the race yet, Collins was pressed by host Judy Woodruff on whether she would endorse Trump later.
“I don’t know. I’m going to have to see what happens between now and then and look at what his record is,” Collins said. “I can’t imagine I would endorse any of the Democrats who are running right now, but I’m going to focus on 2020 in 2020.”
When asked whether she might endorse another Republican, Collins said, “I’m neither ruling it in nor ruling it out.”
During a television appearance last month, Collins said there was “nothing wrong” with Trump facing a primary challenge.
“I see nothing wrong with challengers,” she said on CNN’s “State of the Union.” “That is part of our democratic system.”
Collins has shown a willingness to buck Trump on issues including health care. But last year she provided a key vote in the Senate battle over confirming Trump’s nomination of Brett M. Kavanaugh to the Supreme Court, prompting Democrats to make her Senate seat a top target in 2020.
In 2016, Democrat Hillary Clinton carried Maine over Trump by nearly three percentage points.