Awkward half-endorsements are nothing new for the Donald Trump campaign.

Remember when his onetime presidential rivals started to endorse him? Ben Carson was first, and it was a real head-scratcher: "Even if Donald Trump doesn't turn out to be such a great president. ... We're only looking at four years."

Chris Christie came next; his disposition behind Trump led people to jokingly ask if Trump was holding him hostage.

But Trump's former presidential rivals have largely disappeared from the news in the weeks since Trump became the presumptive nominee, leaving congressional Republicans to endorse him — or not.

That's led to a string of waffling, deflecting and half-answers from members of the GOP who ostensibly support Trump but don't want to get dragged into his latest kerfuffle. Sheriff Joe Arpaio, one of Trump's favorite surrogates in Arizona, called out Republicans this weekend for saying they support the "Republican nominee," without naming Trump.

The two top-ranking Senate Republicans don't want to talk about Trump at all anymore, and even when they did, barely endorsed him. The speaker of the House has had to rebuke Trump repeatedly and publicly for remarks on the campaign trail. And Republican members of Congress who are up for reelection this year have had to make very careful calculations about how openly they support him.

Rep. Elise Stefanik, who represents a district in upstate New York, squirmed in an interview in April in which she was repeatedly asked about Trump. Each time, she had the same answer: "I'm focused on doing my job."

Republicans' reluctance to flat-out endorse Trump was summed up nicely in Sen. Ron Johnson's (R-Wis.) interview with CNN's Dana Bash on "State of the Union" on Sunday. Johnson said he "supports" Trump on issues on which they agree but won't "endorse" the presumptive GOP nominee.

"Support, but not endorse — what's the difference?" Bash pressed. Of course, the answer is that there isn't a difference, other than perhaps a semantic one. But Johnson continued walking his careful line, saying an endorsement should be reserved for someone with whom he agrees on just about everything.

"An endorsement is a big embrace," Johnson said.

An embrace that Republicans just don't seem to want to give Donald Trump.