So here’s where we stood as of Thursday evening: 138 Democrats and independents had called for the appointment of a special prosecutor; just one Republican had joined that call. Another 84 Democrats had called for an independent investigation, joined by only six Republicans.

At this point, in other words, almost an entire party appears to have decided that potential treason in the cause of tax cuts for the wealthy is no vice. And that’s barely hyperbole.

How did a whole party become so, well, un-American? For this story now goes far beyond Trump.

In some ways conservatism is returning to its roots. Much has been made of Trump’s revival of the term “America First,” the name of a movement opposed to U.S. intervention in World War II. What isn’t often mentioned is that many of the most prominent America-firsters weren’t just isolationists, they were actively sympathetic to foreign dictators; there’s a more or less straight line from Charles Lindbergh proudly wearing the medal he received from Hermann Göring to Trump’s cordial relations with Rodrigo Duterte, the literally murderous president of the Philippines.

But the more proximate issue is the transformation of the Republican Party, which bears little if any resemblance to the institution it used to be, say during the Watergate hearings of the 1970s. Back then, Republican members of Congress were citizens first, partisans second. But today’s G.O.P. is more like a radical, anti-democratic insurgency than a conventional political party.

The political analysts Thomas Mann and Norman Ornstein have been trying to explain this transformation for years, fighting an uphill battle against the false equivalence that still dominates punditry. As they note, the G.O.P. hasn’t just become “ideologically extreme”; it is “dismissive of the legitimacy of its political opposition.”

So it’s naïve to expect Republicans to join forces with Democrats to get to the bottom of the Russia scandal — even if that scandal may strike at the very roots of our national security. Today’s Republicans just don’t cooperate with Democrats, period. They’d rather work with Vladimir Putin.

In fact, some of them probably did.

Now, maybe I’m being too pessimistic. Maybe there are enough Republicans with a conscience — or, failing that, sufficiently frightened of an electoral backlash — that the attempt to kill the Russia probe will fail. One can only hope so.

But it’s time to face up to the scary reality here. Most people now realize, I think, that Donald Trump holds basic American political values in contempt. What we need to realize is that much of his party shares that contempt.