Washington — Sometimes idiocy is a form of confession.

With the storming of a secure hearing room, Donald Trump’s strongest supporters in the House essentially admitted their cupboard of personal dignity and rational arguments to be bare. What remains is cheap theatricality and a determination to discredit impeachment by debasing their own institution. The House Republican Iwo Jima turned out to be a seedy carnival sideshow.

But any attention given to the House’s shock troops of inanity and unreason is misdirected. With impeachment now a near certainty, there is only one group of legislators that ultimately matters: the 100 jurors of the U.S. Senate. Of that group, 53 Republicans will have their partisan loyalties tested. And of that group, 20 Republicans — the minimum necessary for conviction — hold the fate of the president in their hands.

What are Republicans in this position thinking? Here is my best guess, based on a few conversations with GOP legislators over the last week:

You moralizing columnists have it easy. I have to live in the real political world. I know President Trump is deeply flawed. But I saw how Democrats and much of the media questioned his legitimacy from the very beginning, making Republicans in my state deeply suspicious about any impeachment process. I don’t think the current process, so far, has been particularly open or fair. And there is a lot at stake. The Democratic Party seems to become more extreme by the day. Ideas like “Medicare for All,” which once were ideological ceilings, have become floors. I think Elizabeth Warren would be a disaster as president, and I really don’t want to do anything to make her election more likely.

Besides, you have no idea what politics is like in my state. The old GOP is gone. Coming out against Trump directly would be seen as an act of treason in the culture war — as a surrender to cosmopolitan socialism. Republicans would never forgive me. And I probably wouldn’t get any credit from the other side anyway. So, at least for the moment, my best option is to remain silent on the substance of impeachment, attack the process and see how things unfold.

I don’t agree with this line of reasoning, but I don’t discount the difficulties faced by Senate Republicans. Utah Sen. Mitt Romney has shown conspicuous political courage in his criticisms of the president. But I understand why other GOP senators would want to be the 10th to break with Trump rather than the second.

The justifications for remaining loyal to the president, however, are increasingly inadequate for a number of reasons:

First, there is the shocking obviousness of the Ukraine quid pro quo. As the testimony of Ambassador William Taylor demonstrated, everyone involved knew exactly what was happening. And the effort to squeeze political benefit out of a foreign government was much broader than a single phone call. The president’s fig-leaf defense — no quid pro quo — has been removed.

Second, there is the foreign policy nightmare of abandoning the Kurds in such a brutish fashion, and then abandoning Syria to Russian influence. This has been a reminder of the real-world consequences of having an impulsive, blathering dolt as commander in chief.

Third, there has been Trump’s predictable turn to racially provocative language (describing his impeachment as a “lynching”) when he gets into trouble.

So, if you are an elected Republican who wants to remain loyal to the president, you need to defend an indefensible act of corruption, explain a massive national security blunder and sacrifice your moral integrity to excuse racism. And add to this the certain knowledge that Trump would not defend you for half a second if it didn’t immediately benefit him.

This creates a political environment in which conviction has moved from impossible to unlikely. The national erosion of Trump’s support has been significant. This has removed the political risk for Democrats moving forward with impeachment. But the removal of the president will probably depend on public opinion among Republicans in 20 red or purple states. In most of such places, at least for Republican officeholders, the political cost of criticizing the president remains high. Growing support for Trump’s impeachment has generally resulted from the hardening of existing opposition, not the wearing away of support in the GOP.

Given the depth and durability of America’s political divisions, and the deep redness of many red states, this may never happen. Yet for Republican senators, the full cost of complicity in Trump’s corruption is becoming clear.

— Michael Gerson is a columnist for Washington Post Writers Group.