On Wednesday, Paul Ryan held a press conference just after the revelation that Donald Trump had pushed James Comey to kill the investigation into Michael Flynn — you know, the guy Trump appointed as national security adviser even though his team knew that Flynn’s highly suspicious foreign ties were under investigation.

Faced with questions about the Flynn scandal and the Comey firing, Ryan waved them away: “I don’t worry about things that are outside my control.”

This might sound like a reasonable philosophy — unless you realize that Ryan is speaker of the House of Representatives, a legislative body with the power to issue subpoenas, compel testimony and, yes, impeach the president. In fact, under the Constitution, Ryan and his congressional colleagues are effectively the only check on a rogue chief executive.

It has become painfully clear, however, that Republicans have no intention of exercising any real oversight over a president who is obviously emotionally unstable, seems to have cognitive issues and is doing a very good imitation of being an agent of a hostile foreign power.

They may make a few gestures toward accountability in the face of bad poll numbers, but there is not a hint that any important figures in the party care enough about the Constitution or the national interest to take a stand.

And the big question we should be asking is how that happened. At this point we know who and what Trump is, and have a pretty good idea of what he has been doing. If we had two patriotic parties in the country, impeachment proceedings would already be underway. But we don’t. What’s the matter with Republicans?

Obviously I can’t offer a full theory here, but there’s a lot we do know about the larger picture.

First, Republicans are professional politicians. Yes, so are most Democrats. But the parties are not the same.

The Democratic Party is a coalition of interest groups, with some shared views but also a lot of conflicts, and politicians get ahead through their success in striking compromises and finding acceptable solutions.

The G.O.P., by contrast, is one branch of a monolithic structure, movement conservatism, with a rigid ideology — tax cuts for the rich above all else. Other branches of the structure include a captive media that parrots the party line every step of the way. Compare the coverage of recent political developments on Fox News with almost everywhere else; we’re talking North Korea levels of alternative reality.

And this monolithic structure — lavishly supported by a small number of very, very wealthy families — rewards, indeed insists on, absolute fealty. Furthermore, the structure has been in place for a long time: It has been 36 years since Reagan was elected, 22 years since the Gingrich takeover of Congress. What this means is that nearly all Republicans in today’s Congress are apparatchiks, political creatures with no higher principle beyond party loyalty.

The fact that the G.O.P. is a party of apparatchiks was one crucial factor in last year’s election. Why did Marine Le Pen, often portrayed as the French equivalent of Trump, lose by a huge margin? Because France’s conservatives were only willing to go so far; they simply would not support a candidate whose motives and qualifications they distrusted. Republicans, however, went all in behind Trump, knowing full well that he was totally unqualified, strongly suspecting that he was corrupt and even speculating that he might be in Russian pay, simply because there was an “R” after his name on the ballot.

And even now, with the Trump/Flynn/Comey story getting worse by the hour, there has been no significant breaking of ranks. If you’re waiting to find the modern version of Howard Baker, the Republican senator who asked “What did the president know, and when did he know it?” you’re wasting your time. Men like that left the G.O.P. a long time ago.

Does this mean that Trump will be able to hold on despite his multiple scandals and abuses of power? Actually, yes, he might. The answer probably hinges on the next few special elections: Republicans won’t turn on Trump unless he has become such a political liability that he must be dumped.

And even if Trump goes, one way or another, the threat to the Republic will be far from over.

In a perverse way, we should count ourselves lucky that Trump is as terrible as he is. Think of what it has taken to get us to this point — his Twitter addiction, his bizarre loyalty to Flynn and affection for Putin, the raw exploitation of his office to enrich his family, the business dealings, whatever they were, he’s evidently trying to cover up by refusing to release his taxes.

The point is that given the character of the Republican Party, we’d be well on the way to autocracy if the man in the White House had even slightly more self-control. Trump may have done himself in; but it can still happen here.