By now, it’s a familiar story. An upstart Republican with no sense of civility makes wild claims about foreigners, attacks critics with abandon and heaps scorn on his party’s establishment. When reporters try to pin him down on his unproven accusations, he responds with even more incredible, incendiary comments. Wildly popular, he cows his political enemies into submission.

Until a woman from Maine stands up in the U.S. Senate to put him in his place.

I am describing, of course, Margaret Chase Smith and her stinging rebuke of Republican Sen. Joseph McCarthy of Wisconsin 66 years ago this week. Smith’s “Declaration of Conscience” was a remarkable act of political courage in the face of a popular demagogue, and her incisive critique could not be more timely today.

In 1950, Smith was a rookie Republican from the small mill town of Skowhegan. The eldest daughter of a barber and a factory worker, Smith entered politics the way many women of her time did: after the death of her husband, whom she succeeded in the U.S. House of Representatives in 1940. She spent four terms in the House before winning election to the Senate in 1948.

Smith was the only woman in the Senate when the relatively unknown McCarthy began making a name for himself with startling claims about Communists working at high levels of the U.S. State Department. Tapping into Americans’ widespread fear of the Soviet Union, the irascible McCarthy became an overnight political sensation. The more outlandish his accusations, the more popular he grew. Few within his political party challenged him.

When McCarthy launched his campaign of character assassination, Smith initially refused to criticize him. A member of the Senate’s Permanent Subcommittee on Investigations, she did some fact-checking and quickly realized McCarthy’s claims were baseless. She decided to end her silent acquiescence.

Smith rose June 1, 1950, to give a speech that she called her “Declaration of Conscience.” She spoke for 15 minutes as McCarthy sat seething two rows behind her. Though she never once mentioned McCarthy’s name, everyone in the chamber — and around the nation — knew who her target was.

“I would like to speak briefly and simply about a serious national condition,” she began. “It is a national feeling of fear and frustration that could result in national suicide and the end of everything that we Americans hold dear.”

Condemning the “irresponsible words of bitterness and selfish political opportunism” that had turned the Senate into a “forum of hate and character assassination,” Smith challenged her colleagues to stand up for principles beyond party. She criticized Democrats for a lack of leadership, but she reserved her harshest judgments for her fellow Republicans. “I don’t want to see the Republican Party ride to political victory on the Four Horsemen of Calumny — Fear, Ignorance, Bigotry, and Smear,” she declared.

Smith’s “Declaration of Conscience” earned her plaudits from the press and cemented her reputation as a substantive woman of courage. Few of her colleagues, however, followed her lead. It would be another four years before McCarthy’s unhinged attacks earned him a censure from the Senate.

Smith’s voice rings with a moral clarity that resonates to our own time. We stand now in a “Margaret Chase Smith moment,” a precarious time that demands political courage, particularly from Chase’s Republican Party. A politician may only get one chance in his or her career to take a morally significant, politically courageous stand for principles that transcend party or policy. This is it.

Today’s Republicans must make their own powerful “Declarations of Conscience” to repudiate a man far more dangerous than Joseph McCarthy ever was.

Uniquely unqualified for the position he covets, self-proclaimed billionaire Donald Trump has engaged in precisely the sort of behavior Smith condemned decades ago. He cultivates fear of Muslims, Mexicans, immigrants and others. He parades his own ignorance and that of his supporters. He revels in religious bigotry, ethnic slurs and misogyny. He gleefully smears his critics with personal insults, belittling nicknames and threats of retaliation.

Yet many Republicans seem unwilling to jeopardize their party’s chances in November by rejecting their party’s presumptive nominee. The senator who now holds Smith’s seat — Republican Susan Collins — admires Smith but has yet to show her role model’s political courage when it comes to Trump. Pressed recently about the candidate, she offered her support, with only a mild suggestion that Trump soften his “tone .”

Faced with a similarly shameless demagogue who undermined the nation’s basic principles, Margaret Chase Smith offered no tortuous rationalizations or timid acquiescence. Instead, she denounced him and pushed her party to do the same. “I don’t believe the American people will uphold any political party that puts political exploitation above national interest,” Smith said. “Surely we Republicans aren’t that desperate for victory.”

Was she wrong?

Chris Myers Asch teaches history at Colby College and is the author of “The Senator and the Sharecropper: The Freedom Struggles of James O. Eastland and Fannie Lou Hamer.”