C’mon. For starters, how many truly “big names” have already endorsed Trump and might conceivably be willing to un-endorse him? (Mark Kirk isn’t a big name.) McConnell and Ryan can’t do it by dint of their leadership positions. McCain, technically a “big name” as a former party nominee, would be taking his political life in his hands with his Senate seat on the line this fall. Your best bet is Rubio, but Rubio’s transparently terrified of risking his chance at another presidential run by turning his back on the party and its nominee this year. We’ve reached the point where Trump could say flat out “I might start a nuclear war” and Rubio, asked for comment, would look constipated and mumble, “Well, he did say ‘might.'”

Even if Rubio surprised everyone by resdiscovering (or discovering) his principles, why would that trigger some seismic shift in support for Trump among party leaders? People would shrug it off on the theory that Marco, being Marco, had simply recalculated that his future prospects would best be served by switching to the anti-Trump side of the equation. There’s no one in the GOP with enough moral authority to pull the rug out from under Trump; if there was, we wouldn’t be in this situation now. It’s time to throw in the towel on these down-by-20-with-two-minutes-left fantasies.

While [Bill] Kristol’s recent focus has been on mounting an independent campaign, he said the possibility of a contested convention is still not out of the question and said there was a conference call on the topic last night…

What is key, Kristol said, to either an independent run or contested convention scenario succeeding would be for a prominent Republican leader, such as House Speaker Paul Ryan or Sen. Marco Rubio, to retract their endorsements of Trump.

“It would be huge, I think you’d have a cascade and then everything opens up,” he said. “Things can’t happen until one key rock gets pulled out of mountainside, or whatever, and then there’s something of a landslide and I really don’t know if that will happen.”

Let’s say it happened. Rubio walks away from Trump, then Cruz declares he won’t support him, then Scott Walker and so on. What effect would that have on the delegates in Cleveland? Potentially … not much:

Stopping Mr. Trump at this point could prove additionally difficult, however, because he has quietly filled the most important convention committees — those that will determine the rules and platform — with delegates loyal to him.

Initially seen as not having a strong delegate whip operation, Mr. Trump can now count on about half the seats on the platform and rules committees, according to Republicans who have been tracking delegate selection. This is a major turnaround from two months ago, when Senator Ted Cruz’s campaign was sweeping the delegate contests.

Even if the delegates are merely split evenly between pro- and anti-Trump, you’d need total solidarity within the latter group plus some defections from the former to make a dark-horse nominee possible. And there are bound to be anti-Trump delegates who nonetheless feel obliged to vote for him because he won the primaries fair and square. It’d be hard, but maybe not impossible, to pull off a coup if we were in the same position we were in circa mid-April, when it looked like the overwhelming majority of delegates in Cleveland would be personally loyal to Ted Cruz. Now, though, you’d have to not only convince the Rules Committee to let the rule governing bound delegates lapse, a ferociously controversial move given that Republican primary voters cast their ballots in the assumption that delegates would be bound, you’d have to actively persuade dozens or hundreds of reluctant delegates to switch sides in voting for Trump as nominee. Knowing what you know about how loyal Trump supporters are to him, do you think Marco Rubio’s un-endorsement is going to change hearts and minds? Do you think Rubio thinks it will? If not, why on earth would he take the risk?

Erick Erickson thinks Trump has two weeks to right the ship or else Scott Walker might be drafted as an alternative candidate. Imagine trying to make that sale at the convention: One of the first men out of the race this year, who crashed last September because he couldn’t get his story straight on immigration of all things, should be installed as nominee in place of the guy who won most of the primaries. Realistically, the only thing that might stop Trump at the convention is if his polling over the next few weeks lands in the toilet and stays there through mid-July. That’s not impossible if Sanders endorses Clinton and lefties unite, but it would have to happen more quickly than everyone expects and Trump would need to trail big to counter the inevitable spin that it’s just a temporary blip while Hillary enjoys a little honeymoon with her party. If he goes down by 12-15, say, that’ll give delegates pause. (If you’re still thinking about a third-party effort instead of a convention coup, poor polling by Trump actually undermines your plan. If the point is to keep him out of the White House, terrible numbers suggests that he’s capable of doing that himself without help.) Relatedly, Patrick Ruffini notes that Trump’s first FEC filing as nominee is due 10 days from now. If his fundraising is conspicuously bad, that too might — might — make some delegates think twice. Although Trump will just say, “I’ll make it all up by being on TV nonstop this fall,” which is plausible. How bad would his FEC numbers need to be for delegates to worry that he’ll lose a media advantage?

Via the Standard, here’s Bill Kristol claiming that Paul Ryan and McCain could galvanize support for a conservative third-party candidate if they got behind an independent candidate and vowed to raise money for him. That’s a party-ending move if it happens, especially if the sitting Speaker is involved. Kristol also tweeted this morning, “Even if GOP convention doesn’t dump Trump, it minimally should insist on its own choice for Vice President, given chance of impeachment.” I assume he’s imagining a Democratic takeover of the House in envisioning Trump’s impeachment. Nothing that’s happened over the past month suggests that a Republican House would stand up to President Trump, no matter what impeachable offenses he might end up committing.