Sen. Susan Collins of Maine says she will not vote for Donald Trump for president, writing in an opinion column that her party’s presidential nominee is unsuited for office because of “his disregard for the precept of treating others with respect, an idea that should transcend politics.”

“I will not be voting for Donald Trump for president. This is not a decision I make lightly, for I am a lifelong Republican,” Collins wrote in a column for The Washington Post on Monday night. “But Donald Trump does not reflect historical Republican values nor the inclusive approach to governing that is critical to healing the divisions in our country.”

One of Maine’s most popular politicians, Collins previously had criticized the New York businessman, but had said she was reserving judgment in hopes he would refrain from the politics of personal attacks, name-calling and misinformation.

Monday night, Collins laid out her case for why Trump shouldn’t become president.

“With the passage of time, I have become increasingly dismayed by his constant stream of cruel comments and his inability to admit error or apologize,” she wrote, citing Trump’s “denigrating comments” about Sen. John McCain, R-Arizona, and Fox News Host Megyn Kelley.

“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. Instead, he opts to mock the vulnerable and inflame prejudices by attacking ethnic and religious minorities. Three incidents in particular have led me to the inescapable conclusion that Mr. Trump lacks the temperament, self-discipline and judgment required to be president,” she wrote.

The first incident Collins outlines was Trump’s mocking of a reporter with disabilities. The second was his claim that a federal judge born and raised in Indiana could not rule fairly in a case involving Trump University because of his Mexican heritage. The third was the candidate’s criticism of the parents of Army Capt. Humayun Khan, who was killed in Iraq.

“It is inconceivable that anyone, much less a presidential candidate, would attack two Gold Star parents,” Collins wrote.

Collins, who had endorsed former Florida Gov. Jeb Bush before he dropped out of the race, had reserved judgment on Trump once it became clear he would be the party’s nominee, saying she wanted to give him more time to moderate his rhetoric and tactics.

“I had hoped that we would see a ‘new’ Donald Trump as a general-election candidate – one who would focus on jobs and the economy, tone down his rhetoric, develop more thoughtful policies and, yes, apologize for ill-tempered rants,” she wrote. “But the unpleasant reality that I have had to accept is that there will be no ‘new’ Donald Trump, just the same candidate who will slash and burn and trample anything and anyone he perceives as being in his way or an easy scapegoat.”

Collins had chastised Trump as recently as last week, when he suggested to a cheering crowd of about 1,900 supporters at a Portland rally that Maine’s Somali-American population had led to a spike in crime, a claim refuted by the police chiefs in Maine’s two largest cities.

Collins’ opinion piece comes three days after state Sen. Roger Katz, an Augusta Republican, made clear he would not be supporting Trump. In his column in the Press Herald on Friday, Katz also criticized Maine’s leading politicians, without naming them, for not taking a stand on Trump.

Although she did not say whom she would vote for in November, Collins made it clear it would not be Trump, noting her patience and hope for a more presidential candidate had expired.

“I am also deeply concerned that Mr. Trump’s lack of self-restraint and his barrage of ill-informed comments would make an already perilous world even more so,” she wrote. “It is reckless for a presidential candidate to publicly raise doubts about honoring treaty commitments with our allies. Mr. Trump’s tendency to lash out when challenged further escalates the possibility of disputes spinning dangerously out of control.”

The Trump campaign did not respond to a request for comment from The Associated Press Monday night.

Trump has now been dismissed by all of the members of Maine’s congressional delegation except U.S. Rep. Bruce Poliquin, a 2nd District Republican who is in a pitched re-election campaign against former state Sen. Emily Cain, an Orono Democrat.

An attempt to reach Poliquin’s campaign spokesman was unsuccessful Monday night.

Poliquin has not directly said whether he supports Trump. When asked for his position, his campaign has issued statements indicating Poliquin is working to create jobs in the 2nd District.

Trump was among 17 Republican candidates to enter the race for the party’s nomination in a race that has been both unusually colorful and unusually confrontational.

It remains unclear how much Collins’ decision not to support Trump will factor into how Mainers vote in November. While noting “that Mr. Trump’s success reflects profound discontent in this country,” Collins also indicated she wouldn’t be supporting Democratic nominee Hillary Clinton.

“As we have seen with the dissatisfaction with both major-party nominees – neither of whom I support – these passions are real and the public will demand action,” she wrote.

A Portland Press Herald poll showed both Trump and Clinton to be widely unpopular with Maine voters.

The same poll also showed Collins enjoyed a 73 percent approval rating among the 475 likely voters who participated in the survey.