Through a combination of wisdom and luck, America has never had to endure the destructive force of a true demagogue and instinctive dictator in the White House. We’ve come close, over the last century, with Democrats Huey Long and George Wallace and Republican Joe McCarthy. But none of them rose high enough to become viable candidates for the presidency.

Now, with the nomination of Donald Trump, the country is faced with a moment of soul-searching. Many of his supporters yearn for the kind of simple yet sweeping promises that Trump has made. Others want a “strong man” in America that will turn the clock back and sweep away those they disagree with.

Moments like this are a test of our national wisdom. The rise of Donald Trump creates a particular dilemma for moderates in the Republican Party. For years, they’ve been trying to broaden the party beyond angry white men. Trump has undone years of that work in a few months.

But his potential destructiveness goes beyond the party to the country as a whole. If you want to see what a Trump presidency looks like, look no further than Paul LePage in Maine. Then close your eyes and imagine Paul LePage as the commander-in-chief of the world’s most powerful military. Now imagine him — or Trump — with their hands on the nuclear codes when someone heckles them from the back of the room.

This is not the first time that Republicans have been confronted with the rise of a demagogue who gathered support around the country but represented a grave threat to the country. The last instance was in the 1950s, when Joe McCarthy was terrorizing the Senate and all who disagreed with him.

McCarthy destroyed lives, reputations and careers through innuendo, guilt by association, overblown charges and ridicule. Trump has relied on all of those things, including outrageous charges that he handpicks from tabloid magazines. But, of course, Trump doesn’t yet have real power.

On June 1, 1950, at the height of McCarthy’s power, a rather small but determined Maine senator rose from her seat to address the Senate with her “Declaration of Conscience” speech. Margaret Chase Smith spoke out against the destruction of decency, tolerance and common values that form the foundation of the American nation.

Sen. Joseph McCarthy sat just two rows behind her.

At that time, McCarthy’s power was expanding daily. Nearly all senators were afraid to speak out against him, for fear of retribution. All except Margaret Chase Smith.

After the speech, McCarthy saw to it that Smith was removed from her standing committee in the Senate, in violation of Senate rules. He later funded her opponent when she sought re-election. Maine people knew better and returned her to the Senate.

Smith’s words travel well through the years because they contain a timeless wisdom, essential to the survival of democracy and a united country. Here are some of the things she said in that hushed chamber that day:

“I speak as a Republican. I speak as a woman. I speak as a United States senator. I speak as an American. The nation sorely needs a Republican victory. But I don’t want to see the Republican Party ride to political victory on the Four Horsemen of Calumny — Fear, Ignorance, Bigotry, and Smear.

“I don’t want to see the Republican Party win that way. While it might be a fleeting victory for the Republican Party, it would be a more lasting defeat for the American people. Surely it would ultimately be suicide for the Republican Party and the two-party system that has protected our American liberties from the dictatorship of a one-party system.

“We are Republicans. But we are Americans first.”

Today, the woman who holds Smith’s seat is another moderate Republican, Susan Collins. And it is her turn to become the modern guardian of Smith’s wisdom, and to find the kind of courage Smith had that day, as she stood in the Senate and changed the course of American history.

Susan Collins says she wants Trump to tone down his rhetoric and act more presidential. Time and reflection can change a person’s character, but new clothing does not. After months of campaigning, it has become impossible to misunderstand what kind of man Donald Trump is, except by turning away. No seasoned political advisers are going to change that.

This is Susan Collins’ moment to rise and speak out against Trump, and place herself into the history books with her own “Declaration of Conscience.”

Alan Caron owns Caron Communications and is the author of “Maine’s Next Economy” (2015) and “Reinventing Maine Government” (2010). He can be reached at: alancaroninmaine@gmail.com