Maine Sen. Susan Collins now faces the most critical decision of her 19-year career in the U.S. Senate: whether to support or oppose the presidential candidacy of Donald Trump.

A month ago, Collins suggested that she could support Trump if he toned down his rhetoric: “I think Donald has shown over and over again that he’s smart enough to tailor his approach. … I think we’re going to see a new stage of this campaign as it starts to go into the general election.”

Sorry, Sen. Collins. You thought wrong.

A few weeks ago, Trump charged that U.S. District Judge Gonzalo Curiel had a conflict of interest in the Trump University case because of his “Mexican heritage.” He repeated his denunciation of the judge last Sunday on “Face the Nation,” challenging the fairness of any judge if they were Hispanic or Muslim. Never mind that Judge Curiel was born in Indiana. Even Republican pooh-bahs such as Mitch McConnell and Paul Ryan thought Trump had crossed the line. While dancing around his reluctant endorsement of Trump, Ryan labeled Trump’s attack “racist.”

Sen. Lindsey Graham, R-S.C., said Trump’s attack was “the most un-American thing from a politician since (Sen. Joseph) McCarthy,” the disgraced Wisconsin senator who used lies and Trump-like smears in his reckless and false “red-baiting” scare of the 1950s. To her credit, Sen. Collins called Trump’s comments “absolutely unacceptable.” However, she kept open the possibility of supporting Trump. She merely suggests that Trump should apologize to the judge and that he should “stop insulting people.”

Wishful thinking, Senator. Asking Donald Trump to apologize to anyone or to stop scapegoating minorities is like asking him to dye his hair green or raze the Trump Tower.

What we are talking about, incidentally, isn’t just a lack of civility on Trump’s part. It is about character and temperament. As David Brooks rightly noted in The New York Times on June 10, “The classic conservative belief … is that character is destiny. Temperament is foundational. Each candidate has to cross some basic threshold of dependability as a human being before it’s even relevant to judge his or her policy agenda. Trump doesn’t cross that threshold.”

Now, in an interview with The New Yorker magazine’s Washington correspondent, Ryan Lizza, Collins has admitted she has reached a turning point.

Rejecting Trump’s reckless views, Collins told Lizza she just might vote for Hillary Clinton in November. “I worked very well with Hillary when she was my colleague in the Senate and when she was secretary of state,” Collins told Lizza in an interview to be published in the magazine June 20. The senator said it is “unlikely” that she would vote for the certain Democratic nominee, but said she was “keeping her options” open.

Sen. Collins can continue to twist herself into a pretzel trying to stand by Trump, no matter the cost to the nation or, in truth, to her legacy. Or she can say, in effect, “Enough.”

Sixty-six years ago, a Republican senator from the state of Maine risked her political career by standing up to a populist demagogue much like Trump. On June 1, 1950, Sen. Margaret Chase Smith took to the floor of the Senate, only two years after her election as the first female senator in the country, and lambasted Sen. McCarthy for turning the Senate into “a forum of hate and character assassination” in his phony and largely baseless campaign against Communists in the U.S. government.

With only limited support from her colleagues who had yet to confront McCarthy’s reckless behavior, Smith denounced McCarthy (sitting two rows in back of her) for his behavior and exploitation of “fear, ignorance, bigotry and intolerance.”

McCarthy survived for four more years of mistreating and demonizing innocent people before the Senate censured him in 1954 after the Army-McCarthy hearings, which led to his defeat.

Smith’s speech was titled “A Declaration of Conscience.” Sen. Collins, now is the time; this is your Margaret Chase Smith moment. You can continue to waffle. Or you can help toss Donald Trump’s quest for the presidency into the dustbin of history.

What say you?