It’s Cruz’s first endorsement from a Senate colleague, but it’s much more than that. It’s a blaring siren to Rubio that it’s time to go.

Lee, a Tea Party stalwart and former Constitutional lawyer, was Cruz’s top Senate ally in the 2013 effort to defund Obamacare, which resulted in a 16-day government shutdown. The episode turned Cruz into a right-wing rock star, but it also earned him many Republican enemies on Capitol Hill, and until now he hasn’t received the endorsement of a single Senate colleague. Lee will be the first sitting senator to formally back Cruz’s candidacy.

Lee opted to stay on the sidelines for most of the 2016 primary race, which has featured three candidates whom he considers to be his closest friends in the Senate: Cruz, Rand Paul, and Marco Rubio.

Rubio is polling well in Lee’s home state of Utah, and his campaign had hoped to score the senator’s endorsement.

I bet it’ll come as a surprise to lots of conservatives who follow politics casually that Lee hadn’t already endorsed Cruz. They’re linked in the public imagination, I think, by their prominence in the effort to defund ObamaCare before and during the 2013 shutdown. Lee is certainly Cruz’s most reliable ally in the Senate. And yet, and yet, he held out on endorsing all last year and through nearly six weeks of primaries this year. That’s because he and Rubio are also frequent allies: They co-wrote a tax bill, for starters, and collaborated on education and transportation reform. They do disagree sharply on the USA Freedom Act, which Lee co-sponsored and which the ultra-hawkish Rubio believes dangerously undermines the NSA’s capabilities, but Lee’s had his differences with Cruz too. And Cruz hasn’t always been tactful in airing them:

When Lee brought up his [criminal justice reform] bill in the committee hearing, he wasn’t sure if he’d have Cruz’s support. But he certainly didn’t anticipate what came next.

Cruz attacked the bill as dangerous and politically poisonous. He said it would lead to more than 7,000 federal prisoners let out on the street. “I for one, at a time when police officers across this country are under assault right now, being vilified right now, when we’re seeing violent crime spiking in our cities across the country, I think it would be a serious mistake for the Senate to pass legislation providing for 7,082 criminals to be released early,” he said. The bill, he claimed, “could result in more violent criminals being let out on the streets, and potentially more lives being lost.”

Cruz went on to warn his fellow senators that if they voted for the bill, they would imperil their careers…

Lee, who was sitting right next to Cruz, could not believe what he was hearing. The bill, he responded, wouldn’t actually release any violent criminals from prison, and its sentence reduction for gun crimes was to reduce the minimum for felons caught with guns or ammunition from 15 years to 10 years—a provision that had once sent a man to prison for 15 years when he picked up a stray bullet in order to clean a carpet.

And yet here we are, five days removed from Rubio’s moment of truth in Florida, and Lee’s throwing in with Cruz. Why couldn’t he have waited another week when he’s already waited this long? Read Sean Davis’s post yesterday at The Federalist and you’ll see. It’s time for anti-Trumpers to give up on Florida and embrace a triage strategy. In all likelihood, Florida’s a lost cause; Rubio won’t win, but enough early votes have been banked for him that even if he dropped today and endorsed Cruz, Cruz probably won’t win either. That being so, the best available option is for Rubio to get out ASAP, effectively conceding Florida to Trump, and clear the conservative and establishment lanes for Cruz and Kasich, respectively, in all of the other states that are voting on Tuesday — Missouri, Illinois, North Carolina, and of course Ohio. Trump will get his 99 delegates in Florida but those four other states will award 259 delegates combined. Without Rubio competing there, Cruz and Kasich will each pick up votes and vacuum up more of those delegates. Remember, Rubio’s presence has already helped Trump inadvertently in several states by holding down Cruz’s numbers while producing little or nothing for Rubio. Cruz likely would have reached 50 percent in Texas, enough to win all of the state’s 155 delegates, had Rubio not been there. By Davis’s count, between Texas, Maine, and Idaho — three states which produced a combined five delegates for Rubio — Trump has won 71 delegates that might have gone to Cruz if Rubio hadn’t been there, enough to make Cruz the overall delegate leader at this point. Now here comes Lee, formally abandoning Rubio to state as loudly as he can that Marco ending his campaign can’t come a minute too soon for the anti-Trump effort.

I’d go as far as to ask this: Given the great risk that Rubio’s campaign would slog on if he wins Florida, continuing to pull votes from Cruz but without enough momentum to actually win many states, should anti-Trumpers actually prefer to see Rubio lose on Tuesday? It’s painful to watch those 99 delegates go to Trump, but if Davis’s math is right then Rubio has already cost Cruz nearly that same amount of delegates across various other states. There are plenty of proportional states still to come too, meaning that Rubio could go on failing to reach the threshold for delegates in each, netting him nothing, while costing Cruz votes that might help him gain on Trump. I’m skeptical that Cruz would beat Trump as handily head-to-head as that WaPo poll this week suggests, especially in northern states, but it’s a better bet than the quagmire the right is faced with now. And if Kasich wins Ohio and hangs around for awhile with Rubio’s centrist voters behind him, that might not be a disaster either in proportional states: Kasich might be able to cut into Trump’s support among moderates in a way that Cruz simply can’t. However it happens, the winnowing needs to happen ASAP. Lee’s doing his part today. Will Rubio listen?

Exit question: Is it possible that Rubio is already planning to quit and Lee knows that? Rubio keeps saying publicly that he’ll fight on but opinion on the right that he’s damaging anti-Trumpers’ chances is creeping closer to unanimity. Maybe he gave his friend Mike Lee the green light to endorse knowing that he’ll be out shortly. Or is that wishful thinking?