What would you say is the primary task of a U.S. congressman? To pass laws? To participate in debates? To sit on committees? I reckon there’s a clue in the oath they swear when they take up their seats. You know, the one about supporting and defending the Constitution of the United States.

The men who drafted that sublime document had no doubt about the first duty of Congress. It was there to constrain the executive, to ensure that no president got too big for his boots, to keep the government answerable to the people. Here is Rep. Justin Amash, R-Mich., putting it beautifully: “Our system of checks and balances relies on each branch 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.”

There was a time when Republicans would have uncomplicatedly cheered those sentiments. Yet when they appeared on Twitter last month, they resulted in Amash being ostracized by his party, challenged in the primaries, and trolled by Donald Trump Jr. (“See you soon Justin ... I hear Michigan is beautiful during primary season”).

Amash’s remarks came in a series of tweets in which he revealed that, having carefully read the Mueller report (unlike most of his congressional colleagues, who started with their conclusions), he believed that Trump’s behavior was impeachable.

I suspect most readers, like most congressmen, have also begun with their conclusions, so there is little purpose in rehearsing the whole argument. But let’s at least allow that a case can be made to the effect that, while there was no collusion with Russia, Trump’s attempts to obstruct the investigation fell short of the standards we should expect from his office.

You can, of course, agree or disagree with that case. But the backlash against Amash has almost nothing to do with the details of the Mueller report. What we are seeing is tribalism at its rawest and ugliest. Amash is howled down, absurdly, as some sort of Democrat fifth columnist, as an attention-seeker, as a man with a personal grudge to settle. In fact, he is sticking to the principle that has animated his entire career — a principle that used to go without saying in the GOP — namely that abuses of power by the Chief Executive must be resisted, regardless of who happens to occupy the White House.

I should add, for the sake of full disclosure, that, though we barely know one another, I have shared a platform with Amash twice. Both times, he spoke with unmistakable patriotism about liberty under the Constitution. Had you told me then that such talk would come to be regarded as suspect in the GOP, I would have laughed. Then again, had you told me that Republicans would soon be arguing that it was fine for their leader to pay off a porn star and lie about it, provided there was no technical violation of campaign finance law, I’d have told you to get lost.

That’s what factionalism does: It makes intelligent and decent people adopt idiotic double standards. As Jonathan Haidt, surely the world’s greatest behavioral psychologist, puts it, it “binds and blinds,” it binds us to “our” team and blinds us to the faults of our teammates.

“Let me warn you in the most solemn manner against the baneful effects of the spirit of party,” was George Washington’s final advice to his countrymen. "It serves always to distract the public councils and enfeeble the public administration. It agitates the community with ill-founded jealousies and false alarms, kindles the animosity of one part against another, foments occasionally riot and insurrection. It opens the door to foreign influence and corruption, which finds a facilitated access to the government itself through the channels of party passions."

The worst form of partisanship is the one tinged with Fuhrerprizip, that is, with the idea that we should follow a leader simply because he is the leader.

There is a perfectly good conservative case for backing Trump on balance, and in general. His character flaws are balanced by tax cuts, deregulation, sound judicial appointments, and so on. But that isn’t what we’re seeing here. What we’re seeing is a “my leader right or wrong” attitude which strikes me as servile and un-American. How extraordinary that a party that calls itself Republican should struggle to make room for a freedom fighter like Amash simply because he is defending the most basic republican virtue of all — namely dislike of the abuse of power.

“A republic — if you can keep it,” said Franklin, who knew how easily people could fall for the cult of a leader. Can you keep it, cousins?

Can you?