For a few months earlier this year, Sen. Marco Rubio seemed to have actually grown a spine. On the campaign trail, he dished out hard truths about Donald Trump, arguing passionately that Republicans would make a historic mistake by nominating the xenophobic, serially dishonest populist.

Then came Rubio's crushing primary defeat in Florida and his flip-flop jump back into the U.S. Senate race. And last night, West Miami's favorite son showed again why he's an Olympic-level political opportunist. In a video message to the Republican National Convention, he encouraged America to vote for Trump.

"Donald Trump is committed to cut taxes, curb spending, and get our national debt under control," he said. "Unlike Barack Obama and Hillary Clinton, Donald Trump takes seriously the threats from Islamic radicals and is committed to rebuilding our military."

Yes, Rubio opted for a video message instead of appearing in person. Yes, he hinted he's not in love with the Donald by never enthusiastically endorsing him. But that kind of weak-kneed half-protest was cast in harsh light a few hours later when Ted Cruz took the stage and went full-out nuclear.

Trump's other Cuban-American presidential campaign opponent made no bones about his feelings in a shocking RNC speech that left the Trump-friendly delegates jeering and booing heavily. He encouraged America to "vote your conscience" while hinting strongly that his own conscience wasn't telling him to Make America Great Again.

Was Cruz's speech self-serving in its own way? Of course. The Texan will surely run again in four years, and by putting his money on Trump flaming out in November, he'll have staked out strong ground as an alternative route for a rebuilding GOP.

But politics aside, Cruz's speech at least had a veneer of honesty and consistency. Cruz, like Rubio, spent months insisting (correctly) that Trump is an unstable circus barker who should never have access to nuclear weapons. There's only one way to follow an act like that, and it's by repudiating that candidate on the brightest stage around.

Rubio didn't do that. He dropped his subtle hints that he still doesn't like Trump, but then he encouraged everyone to vote for the guy.

"After a long and spirited primary, the time for fighting each other is over," Rubio said at the end of his speech.

Cruz left no doubt as to the falsehood of that sentiment.

