He just can't help it. In 2012 it was the "47%" who were losers, now it's Trump supporters. If he pulled his head out of his nether parts he might discover that these so-called "suckers" are probably the same people he pissed off in 2012 and he just threw more fuel on the anti GOP Establishment crowd.
Mitt Romney slams ‘phony’ Trump: He’s playing ‘the American public for suckers’ - The Washington Post
Romney never mentioned in his speech that he had eagerly sought and received Trump’s endorsement in 2012. Ultimately, Romney traveled to Trump’s lavish Las Vegas hotel to hold a news conference and accept his support.
“Being in Donald Trump's magnificent hotel and having his endorsement is a delight,” Romney said the day of the endorsement.