Update: Trump responded to Romney's speech not long after. He said that, "I backed Mitt Romney [in 2012], you can see how loyal he is. He was begging for my endorsement. I could have said ‘Mitt, drop to your knees.’ He would have dropped to his knees.”
In a rambling speech, he called Romney a "lightweight" and a "choker," referring to his loss in 2012 to President Obama.
Romney made no bones about the overarching objective of his speech: “Let me put it plainly: if we Republicans choose Donald Trump as our nominee, the prospects for a safe and prosperous future are greatly diminished.”
It was a full-throated attack on the destructive nature of the GOP front-runner. Everyone knows Trump possesses no actual policy ideas, nor is he the successful businessman he touts himself to be, yet until very recently none of his opponents even attempted to point out his various lies, business failures, empty policies, childish attitude, and horrifically offensive statements.
Romney took it all on in one go. He began with an analysis of Trump’s economic policies, declaring that “If Donald Trump's plans were ever implemented, the country would sink into a prolonged recession.”
Romney’s points were accurate, and equivalent to what most economic analysts have been calling attention to: “His proposed 35% tariff-like penalties would instigate a trade war that would raise prices for consumers, kill export jobs…His tax plan, in combination with his refusal to reform entitlements and to honestly address spending would balloon the deficit and the national debt.”
Romney knew the counterarguments that would come from Trump supporters and addressed them immediately: “But wait, you say, isn't he a huge business success that knows what he's talking about? No he isn't. His bankruptcies have crushed small businesses and the men and women who worked for them. He inherited his business, he didn't create it...A business genius he is not.”
Romney acknowledged that conventional wisdom from history dictates that the race is over at this point, with Trump having definitively won a majority of the primary states. But he says that “the rules of political history have pretty much all been shredded during this campaign”—which is extremely accurate.
He called attention to Trump’s divisive and racist statements about Muslims, which will only fuel ISIS; he reminded us that Trump has mocked a disabled reporter and called war hero John McCain a “loser” for being a prisoner of war; he emphasized Trump’s admiration of Putin and his ambivalence to the Ku Klux Klan.
Romney ended strongly:
“Donald Trump is a phony, a fraud. His promises are as worthless as a degree from Trump University. He's playing the American public for suckers: He gets a free ride to the White House and all we get is a lousy hat.”
Almost everything Romney said during his speech was right on the money. Unfortunately, the only people who will listen to it are moderate Republicans who already support John Kasich, Marco Rubio, or Ted Cruz—Trump’s fanatics will remain loyal to the end.