As Lincoln Michel noted elsewhere in a Facebook post, by strategically supporting Rubio, Cruz, and Kasich in particular states, he's trying to force a brokered convention. By not attacking core conservative principles, and only attacking the person of Donald Trump (and bringing up the probability of Trump losing in November to Hillary), he's inviting the conservative media (i.e., the outlets best positioned to reach Trump's supporters) to re-assess Trump with a much more critical eye.
Maybe it's too little, too late, and maybe it's the exact speech Jeb Bush and other GOP establishment types should have been giving for the last six months, but it's clearly kitchen sink time. But, for now, this speech adds cover to all Republicans who wish to attack Trump. I wouldn't be surprised if Romney or Paul Ryan might enter a late primary contest or two if there's a chance they might legitamtely carry a state.
My favorite moments of the speech include the laughter that greeted Romney when he said, "Donald Trump says he's very very smart." Romney was also effective in pointing out that Trump is not the business genius everyone thinks he is. And then there was that moment where Romney pointed to Trump's recklessness in backing ISIS (!) to overthrow Syria. Plus, I loved how Romney inoculated himself against whatever vitriol Trump is sure to slur him with in the coming hours and days.
Novel update: The "domestic noir" novel I started the other day? Yesterday, I finished the first chapter. Almost 4,000 words in three days. Not bad work either. So now it's on to the second chapter.