This post has been updated with even more Senate Republicans distancing themselves from Trump by essentially predicting he'll lose. An updated version follows. 

Marco Rubio. John McCain. Ron Johnson. John Thune. The Chamber of Commerce for Kelly Ayotte. And now a super PAC with ties to Senate Majority Leader Mitch McConnell (R-Ky.)

At least three potentially vulnerable Senate Republicans, one Senate Republican leader and two influential outside groups think the moment has arrived to basically acknowledge Donald Trump is going to lose the election and campaign instead as a bulwark against a President Hillary Clinton. (House Speaker Paul. D. Ryan (R-Wis.) recently added his name to this list.)

The acknowledgments manifest themselves in the form of "checks and balances" language, and the first Senate Republican to try it out was McCain nearly two months ago, when he won his primary then immediately sat in front of a camera to proclaim he'd act as "a check -- not a rubber stamp -- for the White House."

Sen. John McCain (R-Ariz.) warns that if Hillary Clinton is elected president, "Arizona will need a senator who will act as a check ... for the White House." (John McCain)

As Trump's White House prospects dim, "checks and balance" has been dropped by Senate Republicans in increasingly overt ways. On Friday, CNN reported the U.S. Chamber of Commerce's political arm is running a TV ad in the uber-competitive New Hampshire Senate race urging voters to pick their senator as a check and balance on the White House.

"The hope is that this ad -- the first of its kind -- sends a signal to GOP downballot candidates and other Republican groups that it is time to realize Trump will not win," wrote CNN's Dana Bash.

On Saturday, CNN reported the Senate Leadership Fund super PAC, a group aligned with the most powerful GOP senator, McConnell, is running an ad in Missouri encouraging voters not to elect the Democratic candidate, Jason Kander, because the assumption is that Clinton will be president.

"One Hillary in Washington would be bad enough," the ad says. "Reject Jason Kander."

By ditching their nominee, Republicans are both on familiar ground and in uncharted territory here. Twenty years ago, the party knew Bob Dole was going to lose to President Bill Clinton. Dole knew he was going to lose to Clinton. Thanks to GOP messaging, so did voters: Republicans grew their congressional majority, even as Clinton won the White House with 31 states.

But Dole was a complicit player in this strategy; he even helped campaign for the GOP congressional majorities. Trump is not. He's lashed out at Republicans like McCain and Ryan for dropping him.

Twitter slights from Trump aside, these GOP Senate candidates and operatives think publicly acknowledging the election is over is worth the risk.

They hope they can give disenchanted Republican and independent voters a reason to go vote: Against Clinton. Polls suggest that as much as the voters don't like Trump, they don't like Clinton either. (And that people more and more vote AGAINST something or someone rather than FOR something.)

It's not a perfect option, but many Senate Republicans are calculating it's the only option they have right now. Here's a rundown of the GOP Senate candidates who have said the magic "check and balance" words:
  • Thune (R-S.D.), a member of Senate GOP leadership facing nominal opposition in November, was the latest to say as much: "The states are high," he told my colleague Paul Kane. "I think the Senate is the last kind of check and balance."
  • Johnson (R-Wis.), one of the most vulnerable Republican incumbents this cycle, used almost the exact same language: "Wisconsin will need me to be a check and balance on [Clinton]," Johnson told my colleagues Mike DeBonis and David Weigel in a story that published over Labor Day weekend.
  • The U.S. Chamber of Commerce is running a "checks and balances" ad in New Hampshire for Ayotte.
  • The Senate Leadership Fund super PAC is running a similar ad in Missouri for Sen. Roy Blunt (R).
  • Former Trump primary season rival Marco Rubio blazed the trail on this earlier in the summer. He's still at it.
  • One day after winning his primary, McCain (R-Ariz.) essentially abandoned all hope of Trump winning.

But while this strategy has the potential to lure some moderate Republicans to the polls, it also has the potential to put a drag on the GOP base. There are still many Republicans who think Trump can win — and/or who want him to win. From those voters' perspective, these Republican senators may be calling game over long before it's actually over.

Case in point: A day after Johnson said he'll be a "check and balance" in September a new CNN/ORC poll dropped showing the presidential race a dead heat among likely voters.

The race has since shifted strongly in Clinton's favor.

But even if the facts point to a Trump loss in 18 days, it's still an open question of whether Trump supporters, already skeptical of the Powers That Be, will see it that way. When Rep. Joe Heck (R-Nev.) announced he wouldn't be voting for Trump after The Tape™ came out, he got booed.

Obviously these Senate Republicans would rather not be in this position of ditching their nominee, but a growing number of them seem to think it's the only option they have.