One Republican standing on principle matters. A lot. That’s why Donald Trump is freaking out about the determination by Congressman Justin Amash (R-MI) that the president has engaged in impeachable conduct.

It is not that Amash has reached some staggering conclusion. Everyone who has ever considered the Constitution as anything more than a talking point knows that this president has committed fully impeachable offenses. What matters is that Amash, a conservative with libertarian leanings who has frequently put constitutional concerns ahead of partisanship, is reminding Americans of all partisanships and ideologies that the blank-stare Republicans who currently defend Trump do so reasons of petty politics rather than principle. That’s why Trump calls Amash a “loser.”

In fact, Amash is something very rare these days: a Republican who takes seriously his oath to “support and defend the Constitution of the United States against all enemies, foreign and domestic.”

The Republican Party was founded 165 years ago by abolitionists and land reformers who placed their faith in the radical—if unrealized—promise of America’s founding: that the rule of law might apply equally to all. They rejected the compromises imposed by Southern slaveholders and their Northern allies, refusing to bend to the will of the presidents and partisans who who were making the American experiment into a pale reflection of their own infamy.

At its best over the ensuing decades, “the party of Lincoln” has maintained at least a measure of loyalty to the high ideals of its founding. At it worst, the GOP has not just abandoned those ideals but gone to war against them.

No serious observer of the Republican Party’s recent trajectory would suggest that the party is today at its best. Most Republicans in Congress are shameless sycophants who are more than willing to sacrifice whatever principles they might once have entertained on the altar of Donald Trumpism. But that’s nothing new. American political parties have frequently deferred to their presidents, even when they are abominations.

Most Republicans who served in the House and Senate during the Watergate investigation served as steady defenders of Richard Nixon, and many remained loyal until the bitter end. Much is made of the cooperation that finally evolved on the House Judiciary Committee. But the majority of Republicans sought to protect Nixon. The committee voted on five articles of impeachment against Nixon. None of them received the support of a majority of Judiciary Committee Republicans. Every one f the 17 Republican on the committee voted opposed two of the articles, and their opposition—in combination with that of conservative Democrats—prevented their approval. Of the three articles that were endorsed by the committee, one drew just two Republican votes, while another drew six votes and another drew seven.

Most Republicans did not do the right thing. But the fact that a minority of Republicans stepped up in 1974 proved to be of great consequence. And the threat that a significant number of Senate Republicans would do the same led Nixon to resign rather than fight on.

House Democrats had the courage to challenge Nixon, but they needed—and ultimately received—sufficient Republican support to change history.

These are dramatically different times from the Watergate era. The Republican Party is more rigid and more extreme than it was in 1974. That has led some Democrats in Congress and too many media commentators to imagine that no Republican would dare break from this president, despite the fact that his wrongdoing is far more severe and far more consistent than Nixon’s.

But the doubters were wrong. Amash on Saturday has reminded his party—and his country—that the emperor and his attorney general have no clothes.

After reading the redacted report from special counsel Robert Mueller on wrongdoing by Trump and his associates, the Michigan Republican wrote:

Here are my principal conclusions: 1. Attorney General Barr has deliberately misrepresented Mueller’s report. 2. President Trump has engaged in impeachable conduct. 3. Partisanship has eroded our system of checks and balances. 4. Few members of Congress have read the report.

Amash then detailed his thinking with regard to the attempted whitewash by Attorney General William Barr and explained that “In comparing Barr’s principal conclusions, congressional testimony, and other statements to Mueller’s report, it is clear that Barr intended to mislead the public about Special Counsel Robert Mueller’s analysis and findings. Barr’s misrepresentations are significant but often subtle, frequently taking the form of sleight-of-hand qualifications or logical fallacies, which he hopes people will not notice.”

The Michigan Republican was not confused by Barr’s machinations.

As the first Republican attempted do do in 1854, he went to the heart of the matter: “Under our Constitution, the president ‘shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.’ While ‘high Crimes and Misdemeanors’ is not defined, the context implies conduct that violates the public trust.”

Amash then explained that, “Contrary to Barr’s portrayal, Mueller’s report reveals that President Trump engaged in specific actions and a pattern of behavior that meet the threshold for impeachment. In fact, Mueller’s report identifies multiple examples of conduct satisfying all the elements of obstruction of justice, and undoubtedly any person who is not the president of the United States would be indicted based on such evidence.”

Democrats and Republicans tend to be cautious about impeachment, and Amash acknowledges this. But he tweets, “While impeachment should be undertaken only in extraordinary circumstances, the risk we face in an environment of extreme partisanship is not that Congress will employ it as a remedy too often but rather that Congress will employ it so rarely that it cannot deter misconduct.”

Congressional Republicans like to claim that they are “constitutional conservatives.” For the most part, this is a convenient lie. But, for a rare few Republicans, the Constitution contains truths that remain self-evident. They recognize, as did the founders of the Republican Party, that they cannot be ignored.

It is not necessary to agree with Justin Amash on every issue to respect the sincerity of his observation that “Our system of checks and balances relies on each branch’s jealously guarding its powers and upholding its duties under our Constitution. When loyalty to a political party or to an individual trumps loyalty to the Constitution, the Rule of Law—the foundation of liberty—crumbles.”

Savvy Democrats are already reaching out, including the Michigan Democrat who has had the courage to speak most consistently and most clearly about the need to impeach this president. Congresswoman Rashida Tlaib read Amash’s tweets and responded immediately with an invitation to “come find me in 1628 Longworth. I’ve got an impeachment investigation resolution you’re going to want to cosponsor.”

Let’s hope that Amash accepts the invite. These are the connections by which history is made.