Susan Collins of Maine says she will not vote for Trump

Sen. Susan Collins, R-Maine, announced Monday that she would not vote for Donald Trump in the presidential election, dealing another blow to Trump as he tries to unite his party and win more support from women.

Collins revealed her decision in an opinion column for The Washington Post published Monday evening, saying Trump's proclivity for bullying and invective made it impossible for her to support him. She said she believed having Trump as president would make "an already perilous world" even more dangerous.

[GOP Sen. Susan Collins: Why I cannot support Donald Trump]

Collins is the most senior senator to split publicly with Trump, and her message of censure could send a message to other Republicans that it is safe to shun the party's presidential nominee. She is one of the few moderate Republicans remaining in the Senate and one of only two from New England, along with Kelly Ayotte of New Hampshire, whom Trump, after some hesitancy, endorsed late last week.

Now in her fourth term, Collins also led the Senate committee that oversees homeland security, adding additional weight to her criticism of Trump, who has strained to convince middle-of-the-road voters that he is prepared to serve as the country's commander in chief.

While Collins described Trump as a person who would menace the country's security, she hit him hardest for playing on the country's racial and cultural divisions in the course of the presidential campaign.

Faulting Trump for a "constant stream of cruel comments and his inability to admit error or apologize," Collins specifically mentioned his attacks on Gonzalo P. Curiel, a federal judge born in Indiana whom Trump derided for his "Mexican heritage"; Khizr and Ghazala Khan, the parents of a slain soldier; and a New York Times reporter whom Trump seemed to mock for a physical disability.

"My conclusion about Mr. Trump's unsuitability for office is based on his disregard for the precept of treating others with respect, an idea that should transcend politics," Collins wrote. "Instead, he opts to mock the vulnerable and inflame prejudices by attacking ethnic and religious minorities," she continued.

A spokeswoman for the Trump campaign did not immediately comment on Collins' decision.

On Monday, 50 national security leaders who served in Republican administrations signed a letter rejecting his candidacy, and Republicans including Meg Whitman, a Hewlett Packard Enterprise executive and Republican fundraiser, and Henry M. Paulson Jr., the former Treasury secretary, have broken ranks to back Hillary Clinton.

Collins' opposition will probably make it far more difficult for Trump to compete in Maine, where he campaigned last week in an effort to scoop up at least one Electoral College vote. Collins is a popular figure there and her denunciation can be expected to land with force.

Collins did not say whom she would vote for.