Pro-life and pro-guns Republican senator hints she may support Hillary Clinton over Donald Trump

Susan Collins of Maine said she will not vote for the Republican presidential candidate

Possible support for Ms Clinton might come from the unlikeliest place (AP)

Hillary Clinton has received endorsements from President Barack Obama, Vice-President Joe Biden and Senator Elizabeth Warren – yet the most surprising support might come from one Republican senator.

Susan Collins, the senator of Maine who is pro-life and who voted against background checks at gun shows, said she will not only refuse to endorse Donald Trump as president but she hinted that she may also support Hillary Clinton instead.

The lifelong Republican said she was bothered by Mr Trump’s comments about “Mexican” judge Gonzalo Curiel being “biased” and “unfair” towards him in a ruling about his now defunct Trump University because the candidate planned to build a wall between the US and Mexico.

Ms Collins told the New Yorker that Mr Trump's comments were “an order of magnitude more serious” than anything else he has said, and she had not failed to notice his “troubling insults towards individuals” and his “poorly-thought-out policy plan about banning Muslims from entering the country”.

“This is a difficult choice, and it’s one, like many of my colleagues, that I am struggling with,” said Ms Collins, who is regarded as a more moderate Republican. “It’s not like we have perfect candidates from whom to choose in this election.”

She added she worked “very well” with Ms Clinton when the latter was New York senator and then secretary of state.

“But I do not anticipate voting for her this fall. I’m not going to say never, because this has been such an unpredictable situation, to say the least,” said Ms Collins.

When pressed if there was a chance the lifelong Republican could back Ms Clinton over Donald Trump, Ms Collins replied: “That is true. But I do want to qualify that by saying it is unlikely that I would choose to vote for the Democratic candidate.”

She later insisted that voting for Ms Clinton was “unlikely”, but even considering voting for a Democrat is a first for a Republican senator during the 2016 election campaign.

Many Republicans have either made negative remarks about Mr Trump or have announced they will not back him, including Illinois Republican senator Mark Kirk – who is against de-funding Planned Parenthood – and Texas congressman Bill Flores.

“I was incredibly angry to see Mr Trump question a judge’s motives because of his ethnicity,” Mr Flores, who chairs the Republican Study Committee, said in a statement.

House speaker Paul Ryan, who decided to endorse Mr Trump this month, said the Republican’s comments about Judge Curiel were the “textbook definition of racism”.