The cowardice of Paul Ryan and Mitch McConnell

Earlier this month, Speaker Paul Ryan told what was, in theory, a joke. "Every morning I wake up in my office and I scroll through Twitter to see which tweets I will have to pretend I didn't see later on," he said at the Al Smith Charity Dinner, to appreciative chuckles.

Monday, however, was a reminder that Ryan wasn't kidding. Appearing on WTAQ, a Wisconsin radio station, he was asked what he thought of the indictments Robert Mueller had issued. "I really don't have anything to add other than nothing is going to derail what we're doing in Congress," he said, and he really didn't. Come Monday night, there was nothing on Ryan's web site addressing Mueller's indictments. There was, however, a post summing up his busy month, which was cheekily titled "Not Another Tax Reform Post" and included photographs of Ryan signing bills, handing out medals, and meeting interns.

More From Vox:
Congressional Republicans are helping Trump with a big cover-up
The Manafort indictment is a historic test for American democracy
"A giant fog machine": how right-wing media obscures Mueller and other inconvenient stories

But it's not just Ryan. Senate Majority Leader Mitch McConnell was yet more silent; unlike Ryan, he didn't even make himself available enough to have to dodge any questions. The top story on his website on Monday night — I am not making this up — was "McConnell on IRS Targeting During Obama Administration." There was no mention of Mueller whatsoever.

Imagine, for a moment, that the president in question was not Donald Trump but Hillary Clinton — that it was her campaign chair who had been indicted, that it was her foreign policy adviser who had revealed that he knew of Russia's stolen email cache in advance. Does anyone believe Ryan and McConnell would be so reticent then?

Ryan and McConnell would have you believe they are mounting a courageous defense of Congress's priorities in the face of Trump and the media's distractions — indeed, Ryan framed his comments around precisely that excuse, promising that nothing would "derail what we're doing in Congress."

But these near-daily acts of cowardice and silence are an abdication of Congress's role, not an affirmation of it. The Founding Fathers carried a mistrust of the popular will; they understood full well that the American people might, at some point, elect a demagogue or a knave to the White House, and so they built countervailing institutions capable of binding an errant executive. Congress wasn't meant to ignore a rogue, lawless, or indisciplined White House — it was meant to overwhelm it, to contain it.

"In framing a government which is to be administered by men over men, the great difficulty lies in this: you must first enable the government to control the governed; and in the next place oblige it to control itself," wrote James Madison in Federalist 51. "A dependence on the people is, no doubt, the primary control on the government; but experience has taught mankind the necessity of auxiliary precautions."

Congress is one of those auxiliary precautions. Ambition was meant to counteract ambition. And Congress's ambition, when combined with its power, was expected to be particularly potent — perhaps overwhelming. "As the weight of the legislative authority requires that it should be thus divided, the weakness of the executive may require, on the other hand, that it should be fortified," worried Madison.

But that check is failing today. Ambition is enabling ambition — Ryan and McConnell's ambition to pass tax cuts and hold the Republican base is enabling Trump's ambition to act without proper oversight or sanction. And while Congress has plenty of authority, its leaders are too personally skittish to use it, or even signal that they might use it in the future.

There is much that Ryan or McConnell could have said on Monday to safeguard both the process and the country. For instance: "The details in special prosecutor Mueller's indictments are troubling for anyone who cares about the sanctity of elections. I expect his investigation to run its full course, and he has Congress's full support in this endeavor." And then they could have endorsed one of the bipartisan bills to ensure Trump can't fire Mueller to end the investigation.

Such a move would allow self-preservation as well as courage — if Trump does fire Mueller, it will cause a political crisis on a scale not seen since Watergate, and that will be far more of a distraction from tax reform. But the party has come to bind and blind so effectively that congressional Republicans have lost sight that they, too, have an interest in the political system's fundamental stability, and in telegraphing what behavior will and will not be acceptable from the president.

It is not only Ryan and McConnell who could act to safeguard Mueller's investigation in advance. Sens. Jeff Flake, John McCain, and Bob Corker — all of whom have, at this point, spoken of the threat Trump poses in apocalyptic terms — could join with the Democrats to create a 51-vote majority blocking action on any other bills until, say, the protective legislation introduced by Republican Sen. Thom Tillis was passed. But for all their brave words, they have done nothing of the kind.

This is an extraordinary time in American politics; a test not just of our institutions but of our leaders. And it is a test Republicans are failing. In back rooms and background briefings, they are more caustic and despairing even than liberals; they are not ignorant of the threat Trump represents, nor of the dangers his impulsiveness poses. Those of them who take their conservatism seriously, who consider themselves constitutionalists, who believe the best of their party, feel the injury of Trump's behavior keenly.

But afraid of his wrath, confused by their base, and hopeful that some good can still be wrung out of this crisis, they talk themselves, daily, into small acts of cowardice and silence, and then they find themselves committing big ones, as they are too invested, too culpable, to change their tune now. Trump has humbled them, left them like hungry gamblers deep in a losing streak; they need a win, they need something, so they can justify all they have already done, all they have already excused.

In their hearts they know better. In 2010, then-Rep. Paul Ryan published a book called Young Guns. In the introduction, he wrote something both eerily prescient in its language and notably damning in its specifics.

"People think that their country is slipping away from them," Ryan said. "They think that their future is not going to be as bright. So they're ready to embrace a reclamation of what made this country great. And if we get back into the majority we cannot fall from this fight. We can't be intimidated. We can't worry about the demagoguery and the negative ads we're going to get."

The country did want to be made great again. And that impulse propelled Republicans back into the majority, and Ryan into the speakership. But here he is, today, terrified of a demagogue, hiding from the negative ads he might get, letting down a country that needs more from him.

Commentary by Ezra Klein, the editor-at-large and co-founder of Vox. Follow him on Twitter @ezraklein.

For more insight from CNBC contributors, follow @CNBCopinion on Twitter.