If Donald Trump were to come back to beat Hillary Clinton in the contest for the White House, it'd be the biggest late comeback in the history of presidential polling. But amazingly, Senate and House Republicans have managed to avoid falling down with him.

That could change. Trump's numbers are teetering on a precarious edge, and so are Republicans who have to share the ballot with him. Many political observers think if Trump is down by 10 points or more in states with competitive Senate and House races, those candidates will have a nearly impossible time hanging on.

And Trump could be headed in that direction. A new Washington Post-SurveyMonkey poll of 15 battleground states finds Clinton with a clear lead in nine of them.

Which is why Wednesday's third and final presidential debate is yet another nerve-racking moment for GOP candidates. Their campaigns could depend on whether Trump can stabilize his.

But what does “stabilizing” look like from the perspective of the erratic Trump campaign? We talked to some GOP political operatives and picked our own brains for a list of dos and don'ts. (Will Trump follow them? That's another question entirely. History says no.)

Which reflects the hope-and-pray position Republicans are in right now. They can't control Trump, but they can wish upon a star that he will follow these key rules to save Republicans from himself:

DO: Talk about the economy

There's a reason House Speaker Paul D. Ryan (R-Wis.) spends most of his time talking about pocketbook issues, such as comparing his tax plan to that of Democrats. Because it polls well among voters, especially when Republicans talk about it.

The economy is consistently atop voters' lists of concerns — at the end of September, 33 percent of independent likely voters rated the economy as their top issue when voting for president, according to Washington Post-ABC News polling in September.

And right now, Americans are giving Republicans higher marks on handling their top problem than Democrats, as in this September Gallup poll:

DO: Talk about Obamacare

The moment is ripe for Trump to go on the offensive here. Even some Democrats are openly talking about how expensive health care is right now. Minnesota's Democratic governor recently said the Affordable Care Act is “no longer affordable” for many in his state. Earlier this month, Bill Clinton referred to Obamacare as “the craziest thing in the world” as health insurance premiums spike and major providers leave the system. (He later tried to back off that statement.)

Hillary Clinton says she would fix what's broken; Trump walks the Republican line of repeal and replace — replace with a vague, less-expensive system that he has yet to describe. Given Obamacare's public relations troubles so close to the election, detailing the “replace” part would be a smart move for Trump to make now.

(One caveat: This isn't a surefire win for Trump: A September Post-ABC poll found that Americans are split evenly on which candidate they trust to handle health care, 47 percent for Clinton and 46 percent for Trump.)

DON'T: Talk about Bill Clinton's accusers

For one, it opens the door for Hillary Clinton to talk about Trump's accusers. Two, the attacks don't seem to be sticking.

In a new October Post-ABC poll, two-thirds of voters said they didn't think Bill Clinton's treatment of women was a legitimate campaign issue.

Three, it's totally unclear whom Trump is winning over by playing the “Bill Clinton was much worse than me” game.

“Anybody who's been offended by Bill Clinton's indiscretions has been offended for 25 years,” said Josh Holmes, a Senate Republican strategist. “You're not going to pick up the center of the electorate based on something people have digested and understood for more than two decades.”

DON'T: Get baited by Clinton again

Republicans say Trump absolutely cannot afford another week of being sidetracked by a battle with a Latina beauty queen or some other distracting-yet-politically-problematic ghost from his past that Clinton might dredge up.

The last time that happened, -- after Clinton mentioned Trump's beef with former Miss Universe Alicia Machado in the first debate in September — Trump spent a week going after Machado, basically the exact opposite of what he needed to do, given his deficits among women and Hispanics.

Unfortunately for Republicans, Trump has proved unwilling or incapable (or both) of staying on message, especially when Clinton tries to knock him off it.

And therein lies the problem for nervous Republicans watching Wednesday's debate: They can't control what Trump says or does. That means vulnerable Senate and House Republicans can run the most perfect campaigns in the world, but if Trump bombs his, they might be going down with him.