CLEVELAND – Republican conventions, even those as relatively slapped-together-at-the-last minute-seeming as this one, are highly choreographed and scripted affairs where surprises are few and far between.  

Ron Johnson, who cultivates a pretty unsurprising and plainspoken affect when he’s at the Capitol as Wisconsin’s senior senator, has created one of the more curious “wow” moments as the week opens.  

His change of heart over the weekend, when he agreed to make a speech to the delegates in prime time Tuesday night, means his podium appearance will be the only one by the nine GOP senators in any real danger of defeat this fall.  

He had promised for weeks to stay home and on the campaign trail, where he’s said he supports but does not endorse Donald Trump. It’s a position that had seemed to make palpable sense, given that he’s an underdog in his rematch against Democrat Russ Feingold, whom he ousted from the Senate six years ago.  

But it will be an impossible middle ground to hold once he appears at Quicken Loans Arena. GOP operatives and party leaders in the state said Monday that it was becoming increasingly sensible politically for Johnson to embrace Trump’s coattails, because the likely nominee is expected to make a genuine effort to win enough of Wisconsin’s white male voters to secure the state’s 10 electoral votes. That would mark the first GOP victory since the Reagan re-election landslide of 1984.  

“I’m not worried about him coming at all,” declared Kelly Ruh, a delegate from Green Bay and Johnson campaign organizer. “It’s time to unify the party, that’s starting to happen and it’s the obligation of our party leaders to set forward to be part of that.”  

She volunteered, however, that Johnson would be returning home to campaign within hours of delivering his speech.  

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Ruh’s comments echoed what a national GOP officials, speaking on background, said was the ultimately persuasive pitch made to Johnson by fellow by Wisconsinite Reince Priebus, the chairman of the Republican National Committee.  

Johnson’s change of heart was unexpected enough that one of his closer collaborators in the Senate, Susan Collins of Maine, said “that sounds like it must be a rumor” even after the Trump campaign unveiled its roster of Tuesday night speakers .  

What Johnson will talk about isn’t clear, because the convention’s rhetorical theme for the evening is supposed to be economic growth and job creation but the senator’s campaign says he was asked to talk about the domestic threats posed by radical Islamists and other terrorists overseas. Johnson is qualified to talk about both, because he ran a successful plastic packaging business before coming to Washington and has been chairman for the past 18 months of the Homeland Security Committee.  

Either way, he’ll probably have the benefit of a “hot” hall. He’ll appear right after a video called “Hil-LIAR-y,”  designed to highlight some of the trustworthiness issues that so many GOP delegates find so galling about Trump’s opponent. She is expected to be nominated by the Democrats in Philadelphia next week.  

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Feingold spokesman Michael Tyler used the dishonesty line of attack against Johnson, contending that the senator had undone his promise to avoid the convention because he “couldn’t resist rubbing shoulders with his corporate supporters, Washington insiders and Donald Trump.”  

The tartness of the retort was yet another reminder about why all the other politically vulnerable GOP senators are steering clear of the convention hall this week – if not Cleveland entirely.  

Marco Rubio, who made a last-minute decision to seek a second term in Florida but is no better than an even bet to win, agreed to address the convention Wednesday night – but only on a prerecorded video.  

Rob Portman, the senior senator from the host state of Ohio, has filled his week with campaign events including several in the Cleveland area. Warding off a stiff challenge from former Gov. Ted Strickland, Portman has opted to steer clear physically of the Republican National Convention for the first time since 1988.  

Roy Blunt, similarly, hasn’t missed any of the previous four conventions. But he’s in an increasingly close contest against Missouri Secretary of State Jason Kander and so is spending this week crisscrossing the state, touting his hand in the recent enactment of a law designed to bolster the federal fight against the deadly opioid epidemic, one of the few notable bills Congress has cleared this election year.  

The same is true for Portman, Kelly Ayotte of New Hampshire and Patrick J. Toomey of Pennsylvania – all of whom are facing serious challenges from popular Democrats in states President Barack Obama carried twice.

John McCain, the 2008 GOP presidential nominee, is spending the week in Arizona in part because his views of Trump (who questioned McCain’s standing as a war hero a year ago this week) involve damning with the faintest of praise and in part because Rep. Ann Kirkpatrick represents a viable threat to McCain serving a sixth term.  

Only one of the GOP incumbents in danger — Mark S. Kirk, who like Johnson is now more likely than not to lose his seat — has gone so far as disavowing Trump as the nominee, however. He, of course, is staying away from Cleveland this week, as well.