Paul Ryan is the most promising politician to become the most disappointing.

Have you seen him lately? Is he hiking the Appalachian Trail? Has he taken up Pilates? Does he have a swim meet he needs to get to?

I ask all in earnestness, because — breaking! — the executive branch of the federal government of the United States of America is collapsing due to its leader being dangerously unstable.

The head of state is caught in a self-amplifying loop of destructive scandal, and one manifestation of his condition is that the more threatened he feels the more erratic (and dangerous) he becomes.

Here is another fact: The Constitution of the United States of America provides for a system of three co-equal branches of government designed to check each other. Paul Ryan is the head of one of the houses of one of those branches. He is also the closest thing to a leader the Republican Party — the majority party, the party of the president — has in Washington.

The president of the United States is implicated in several scandals that require independent investigations that will probably reveal improprieties that justify his impeachment. Not on political grounds. But on criminal and personal grounds.

Meanwhile, the speaker of the House is nowhere to be seen. His majority leader is cracking jokes about the president of the United States being on the payroll of the thug leader of a hostile, nuclear-armed foreign power. Ha ha!

No, wait, we've found him! Here's Paul Ryan at a press conference looking every bit the ISIS hostage, saying he has "confidence" in Donald J. Trump.

This is a sick, sad joke.

I genuinely believe that Paul Ryan is an intelligent man who went into politics with the intent of serving his country and improving the state of policy, not to aggrandize himself. But I would like a better explanation for this behavior than the absolute cliché of the idealistic young man who goes to Washington intending to change the system and, corner cut after corner cut, becomes the system.

What makes this sick, sad joke especially poignant — and it has been this way since Trump's entrance into national politics — is that Ryan isn't even putting his political interests over principle. The longer Trump is associated with the GOP, the more he tarnishes it. The chances are good that the GOP will lose its majority (and therefore, Ryan his gavel) in 2018, and very good that it will lose the White House in 2020. The odds of both enacting a Republican agenda and winning national elections are much better under a President Pence than under a President Trump.

Of course, that's not why Ryan should be trying to investigate Trump and eventually start impeachment proceedings. He should be doing it because it's the right thing to do.

Like so many Serious Conservative Wonks™, I once admired Paul Ryan deeply, as a man of ideas and principle, an architect who could build my and my fellow travelers' vision of a limited government that empowers civil society and creates broadly shared prosperity.

And I have to say this in his defense: He has one of the world's most impossible, thankless jobs. His caucus is fractured, his base doesn't know what it wants, and did I mention there is a crazy person in the White House?

Once Trump was legitimately elected to the White House, Ryan had a civic duty to give him a chance and try to work with him. But now it is beyond a doubt that Trump is as unfit as he seemed during the campaign, that he has shown absolutely no indication of "growing into the office," and that attempts to "corral" his negative influence by surrounding him with savvy establishmentarians has not prevented him from outing sensitive intelligence operations to the Russians or likely committing obstruction of justice.

If Paul Ryan cares about the country, or his majority and agenda, he needs to stop defending Trump — and start investigating him.