WASHINGTON (CBS/AP) — Sen. Susan Collins, one of the most moderate Republicans in the Senate, said Monday she 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 an op-ed column in The Washington Post. “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.”

Collins also said she does not support Trump’s rival, Democrat Hillary Clinton.

Photo credits Sen. Susan Collins and Bill Pugliano/Getty Images

Photo credits Sen. Susan Collins and Bill Pugliano/Getty Images

The Trump campaign did not immediately respond to a request for comment.

In the essay posted Monday night on the Post website, Collins wrote that, over time, she has “become increasingly dismayed” by Trump’s “constant stream of cruel comments and his inability to admit error or apologize.” Three incidents led her to the “inescapable conclusion that Mr. Trump lacks the temperament, self-discipline and judgment required to be president.”

They include his apparent mocking of a reporter with a disability (Trump says he wasn’t mocking the man), his criticism of a judge’s Hispanic heritage and his criticism of a Muslim family whose son was killed fighting in the Iraq War.

“It was his attacks directed at people who could not respond on an equal footing — either because they do not share his power or stature or because professional responsibility precluded them from engaging at such a level — that revealed Mr. Trump as unworthy of being our president,” she wrote.

Collins said she also was dismayed that Trump minimized the heroism of Sen. John McCain, a prisoner of war in Vietnam for five years, and insulted Fox News host Megyn Kelly in a debate a year ago.

“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.”

Her column was published the same day Trump sought to reset his struggling campaign with an unusually disciplined speech in Detroit and reassure Republicans unnerved by a string of feuds he started in recent days.

Before the night was through, though, he tweeted that “many people” are saying Clinton is linked to the execution of an Iranian scientist. A Clinton campaign aide responded, “‘Many people are saying’ = ‘I made this up.'”

(TM and © Copyright 2016 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2016 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)