Both Cruz and Rubio have suffered from a "mini-me" draining votes from them. For Cruz, that was Carson, who has since dropped out. For Rubio, that's Kasich. The difference is, Kasich was much more effective at choosing his battles and targeting his Bigger-Me, whereas I'm still not sure what Carson thought he was doing with his campaign.
Brilliant to give Trump 99 Free delegates? I don't think so. Vain, maybe. For those of us who prioritize Trump Not Winning over one of the two conservatives being the particular one to win, it's infuriating. Cruz is extremely unlikely to win Florida, all he is doing is continuing the fratricidal war among the not-Trumps that we have seen starting in New Hampshire, to Donald Trump's advantage. To the credit of both men, they have not done so on the debate stage.
Ted Cruz is currently assessed as having a less than 1% chance of winning Florida. Rubio, at least, has a 40% chance.
You are right that Trump is dropping. In Florida, however, undercutting Rubio doesn't mean that Cruz wins. It means that he protects Trump.
For the same reason, even though I personally find the man extremely grating, annoying, cowardly, and blatantly self-serving, neither man should target Kasich in Ohio, but rather target him everywhere else where the delegates are proportional. You don't give Donald Trump large blocs of delegates at this stage.
Oh yeah, if either don't win their states, their chances of winning the 1237 go from small to vanishingly nothing. Kasich has already admitted he can't get to 1237, and is now playing spoiler in hopes of being able to pull in as Trump's VP.
I read the op-ed and that 4 senators will be endorsing. I'm tempted to name Sasse and Lee off of straight ideological closeness, but honestly have no idea. If he's smart and trying to really cripple Rubio's steam, it will include someone that should have been a Rubio-backer, rather than simply a Who's Who of the big name conservative types. Part of me hope that Sessions is one of them after Trump declaring his Flexibility... and part of me has decided that the act of endorsing Trump is an irrevocable deed, and that whomsoever does so should be punished. Forever.
My dream at this point would be for Rubio and Cruz to announce that they will support at the convention whichsoever of them comes with the most delegates, and spend the rest of the campaign utterly smashing Trump and Kasich (in every state but Ohio). Then let the best man be at the top of the ticket, and the second be VP.
But that would require that politicians seeking the POTUS slot cease being self-interested actors convinced of their own necessity and put the country's benefit ahead of their own... so.... probably out of luck.