President Trump listens during a meeting with North Korean defectors in February. (Jabin Botsford/The Washington Post)

The conventional wisdom is that the week-long Kelly Sadler drama was an unforced error — that the White House unnecessarily prolonged the situation by drawing a line in the sand and refusing to apologize.

But Tuesday showed precisely what President Trump got out of the whole affair: a power move.

The Washington Post's Seung Min Kim reports that, when Trump visited Capitol Hill on Tuesday, GOP senators declined to even broach Sadler's behind-closed-doors comment about how Sen. John McCain (R-Ariz.) was “dying anyway.” Even as many of them publicly called on the White House to apologize, when given the chance to actually make the case to him personally, they conspicuously opted not to.

They offered a series of justifications for letting the whole thing slide. “I think everybody involved should apologize,” Sen. John Neely Kennedy (R-La.) said after the lunch with Trump. “But this was a policy meeting, right? It was policy-driven.” Sen. Bob Corker (R-Tenn.), a sometimes Trump critic, explained: “That’s not what we do in those meetings.”

A more honest explanation would be: Trump holds all the cards in our relationship.

The episode epitomizes the one-sided relationship between the supposedly co-equal branches of American government. Trump's power over the Republican base has once again brought GOP senators to heel over something that clearly bothered them. When the 2016 campaign began, they decried Trump for questioning McCain's war hero status. Today, they can barely muster a whimper when a White House aide talks blithely about the death of their own brain-cancer-stricken, war-hero colleague. Those two bookends are extremely telling when it comes to who's in charge here.

Imagine being McCain or a member of his family and seeing your colleagues back down in the face of the mighty Trump over this whole thing? Even if the meeting was about policy, it presented a unique face-to-face opportunity to try to prevail upon Trump to do something that GOP senators believed on almost a consensus basis that the White House should do. The fact that they didn't bring it up speaks volumes. And Trump must know just what it says about his power to control lawmakers.

And here's the thing: Their calculation makes sense. The same day they passed on confronting Trump over the McCain episode, they confirmed their sixth U.S. Court of Appeals judge in just one week. They've got a Supreme Court justice and could soon have another who might tip the balance of that court for decades to come. They got tax cuts that their base (and donor base, of course) loves. And while their congressional majorities are certainly in jeopardy in November, even that's looking less perilous now.

We've also seen repeatedly just how bad it is for one's career to question Trump. Corker, who is retiring, saw his numbers plummet when he bashed Trump. Sen. Jeff Flake (R-Ariz.) admitted he couldn't win reelection because of his criticism of Trump and decided not to even run. Trump's attacks on Sen. Mitch McConnell (R-Ky.) have pushed the majority leader to new levels of unpopularity.

Another person who has been on the short end of this relationship with the GOP base is McCain himself. And that made it particularly difficult for GOP senators to draw their own line in the sand here. Republican senators struck a perhaps-unspoken bargain with Trump that they would turn something of a blind eye to his misbehavior, in exchange for conservative progress. And it has largely worked.

But we saw the ugly side effects of that arrangement over the past week. And it was pretty ugly.