The Post offers us a history lesson today. Jeff Flake’s speech yesterday reminded Kevin Kruse, a professor of history at Princeton, of Senator Margaret Chase Smith’s “Declaration of Conscience” address to the Senate on June 1, 1950.

Like Flake, Smith (R-Maine) spoke to denounce a demagogue in her own party and to announce her refusal to stand quietly by as he did damage to the nation’s institutions. Smith’s target — unnamed in her speech, much as Trump was unnamed in Flake’s — was none other than the junior Republican senator from Wisconsin: Joseph R. McCarthy.

A few months earlier, in February, McCarthy had set the political world on fire with his stunning accusation that there were 205 “known communists” working in the Truman State Department. Challenged on his charges, McCarthy repeatedly refused to offer any proof; indeed, in later versions of the speech, he even changed the alleged number several times over. But no matter. McCarthy’s charges made for spectacular headlines and, as he discovered, fame brought with it a rise in his political fortunes.

Fame and lying. Very Trump. No wonder Roy Cohn was Trump’s mentor.

For his Republican colleagues in the Senate, McCarthy posed a bit of a problem. The GOP had been wandering in the political wilderness for the previous two decades, cast away by voters who blamed them for the Great Depression and rallied to the party of Franklin D. Roosevelt during the New Deal and World War II. At long last, McCarthy had provided a popular cause that might let them tear down the Democrats and build themselves up instead.

Some of them were delighted; others were unhappy about the evidence-free accusations.

Though she was a freshman senator, and the only woman in a male-dominated body, Smith decided she had to speak out. (As she made her way to the chamber, she ran into McCarthy himself on the Senate subway. “Margaret, you look very serious,” he joked. “Are you going to make a speech?” “Yes,” she shot back, “and you will not like it!”)

With McCarthy and their colleagues arrayed around her, Smith noted with sadness that the Senate had been “debased” in recent months by a new politics of “hate and character assassination.” “I think that it is high time for the United States Senate and its members to do some soul-searching — for us to weigh our consciences — on the manner in which we are performing our duty to the people of America,” she announced.

Smith was, as she noted in her remarks, a loyal Republican and a proud partisan, one who had criticized Democrats repeatedly in the past and would continue to do so in the future. But partisanship had its limits, she insisted: “I don’t want to see the Republican Party ride to victory on the Four Horsemen of Calumny — Fear, Ignorance, Bigotry, and Smear.”

There’s also lying. McCarthy lied; Trump lies.

Speaking out against McCarthyism was a patriotic duty for all good Republicans, Smith asserted, in part because McCarthy had presented his own actions as patriotic. “Those of us who shout the loudest about Americanism in making character assassinations,” she said, “are all too frequently those who, by our own words and acts, ignore some of the basic principles of Americanism: The right to criticize; the right to hold unpopular beliefs; the right to protest; the right of independent thought.”

Those are also of course basic principles of liberalism, in the classic sense that Republicans can defend just as passionately as Democrats can. They are among the founding principles of the United States (with the tragic stipulation that they didn’t apply to slaves or Native Americans or, mostly, women), but they are also principles of many other countries now and of the UN at least on paper.

The Senate was largely stunned by the speech. Most expected McCarthy to return the attack with his usual ferocity, but he glared at the back of Smith’s head for a while and then abruptly stormed out of the chamber. A few colleagues muttered comments of support, but the Republican leadership largely looked the other way.

No Twitter then. No way for McCarthy to tell his millions of followers what a loser Smith was.

Pundits like Lippmann and Baruch praised her speech, but it made no difference.

But despite the widespread praise, Smith’s declaration did nothing to stop McCarthy. Publicly, the Wisconsin Republican continued to ignore her. When pressed, he responded, “I don’t fight with women senators.” Privately, McCarthy mocked Smith and her supporters as “Snow White and the Six Dwarfs.” One of the men who signed Smith’s Declaration, he joked, had been caught “speaking through a petticoat.” Within weeks, the debate over the Declaration of Conscience was swept aside by the outbreak of the Korean War. With a new Cold War crisis abroad, McCarthy and McCarthyism grew steadily stronger at home. Emboldened by his reelection that fall and the electoral success of his supporters, too, McCarthy finally had his revenge in 1951. He kicked Smith off the prized permanent investigations subcommittee he chaired, replacing her with a Republican rising star who shared his anti-communist commitments: Richard M. Nixon, then a senator from California.

That worked out well.

McCarthy was able to do a lot of damage from then on, until he made the beginner’s mistake of going after the Army; at that point the Senate finally censured him.

Today, Smith’s “Declaration of Conscience” stands as a piece of stirring rhetoric, but also a stark reminder that words can only do so much. It is not enough to speak out against threats to the nation, to give voice to one’s conscience. Convictions ultimately mean little, if there are no actions to match them.

Flake’s words echo Smith’s, but they ultimately ring even more hollow. Though Flake has spoken out against Trump consistently, he has also regularly voted to support the president’s agenda on issues ranging from health care repeal to the budget to the Supreme Court. Indeed, only hours after his principled stand in the Senate, Flake fell back in line that same night, providing a crucial vote against a consumer protection measure that brought the Senate to a 50-50 tie, and a tiebreaker by Vice President Pence. For all his valiant words, he’s only given the president another victory.

Oh yes?

Yes. That’s for another post.