Raising President Bill Clinton's past marital infidelities is the surest way to transform Hillary Clinton into a sympathetic figure and boost her prospects.

That's the assessment of veteran Republican strategists who are watching with alarm as Donald Trump moves to blunt the Democratic nominee's post-debate momentum by reminding voters that Bill Clinton cheated on his wife.

Hillary Clinton has been battered by scandals and had difficulty connecting with voters. Her personal approval ratings are nearly as low as Trump's, resulting in a competitive race down the stretch.

But Republicans worry that Trump might do for Clinton what she has had trouble doing for herself: rehabilitate her image and grow her narrow lead, if his campaign insists on rehashing Bill Clinton's decades-old affairs.

"I would not do it," Republican insider Charlie Black told the Washington Examiner.

"He is not running against Bill Clinton, who is more popular than Hillary Clinton," he added. "In the past, she has come across as a sympathetic figure whenever his indiscretions have been raised."

Afforded anonymity in order to speak candidly, a second Republican operative was more blunt in his criticism of Trump's strategy to undercut Clinton by discussing her husband's foibles: "It's stupid."

Republicans in Washington aren't necessarily in lockstep behind Trump. But they do care if he's competitive with Clinton. A close race makes it more likely that Republicans hold their Senate majority and minimize their losses in the House.

The Republican strategists interviewed for this story worked in D.C. in the 1990s, during Bill Clinton's two terms in the White House. They remember vividly how the GOP overreached in relentless pursuit of spotlighting the president's infidelities, in particular, his acknowledged affair with a White House intern.

Republicans blame the episode for costing them five House seats in the 1998 midterms, an unexpected development after then-Speaker Newt Gingrich, now a top Trump supporter, assured them that Clinton's indiscretions would lead to big gains in that election.

Hillary Clinton, never the most popular first lady, also benefited. Just two years later, she moved to New York and defeated a Republican congressman for an open Senate seat. Clinton won by more than 12 percentage points.

"When people bring up Bill's infidelity, it increases their confidence in Hillary," Liz Mair, a Republican strategist, said in an email. "Their logic is: 'If she can put up with that … and still keep moving forward, she can stick it out through the most challenging circumstances of the presidency.'"

Trump on Monday turned in a subpar performance in the first presidential debate. Clinton dinged the New York real estate developer on his questionable business practices and the implications of his refusal to release his tax returns.

But the attack that has received the most post-debate coverage — and what really irked Trump — was Clinton's charge that the Republican mistreats women.

Clinton did so by highlighting accusations, essentially confirmed by Trump, that he once referred to a Hispanic Miss Universe contestant as overweight and "Miss Housekeeping."

The day after the debate, Trump and his high-profile surrogates responded by subtly raising the specter of Bill Clinton's affairs.

It began with Trump's son, Eric, saying in a radio interview that his father had shown restraint and compassion by not discussing the matter during the debate, with Clinton's daughter Chelsea sitting just a few feet away in the audience.

Gingrich echoed that message, calling Trump a "gentleman" for holding back. Trump-friendly media outlets, like Breitbart News, whose executive chairman Steve Bannon is now CEO of the Trump campaign, joined in to help push the attack.

Then, the Wall Street Journal reported that Trump campaign was issuing talking points instructing its broader universe of supporters how to handle the subject if asked by reporters.

No, the affairs weren't her fault, they are to say, but Clinton has been "an active participant in trying to destroy the women who [have] come forward with a claim."

On Thursday, Trump pushed the attack more explicitly.

He criticized the Clintons' "sordid" past during a campaign rally in New Hampshire and, when asked in an interview with New England Cable News why Bill Clinton's misdeeds would reflect on Hillary Clinton, said: "Well, you'll have to figure that out. I think it's pretty simple to figure that out."

Some Republicans suspect that Trump revived the matter to play mind games with Clinton and lead her to believe he plans to raise the topic their second debate on Oct. 9. They believe there could be some strategic utility in this approach, if it's nothing more than a head-fake.

And that's all it's likely to be, some Republicans believe. Trump's campaign manager is Kellyanne Conway; she's an experienced pollster who knows that hammering Clinton on something her husband did could cost the GOP nominee votes among undecided and moderate female voters.

That was the conclusion of a Republican-run focus group conducted last year, to test how voters would react to attacks on Clinton by way of talking about her husbands' infidelity. "These attacks turned Hillary into a victim and … engendered sympathy for her," GOP strategist Tim Miller told NBC News.

Republicans also question the strategy because it distracts Trump from the message most likely to carry him to victory; that he's a Washington outsider, versus a 20-plus year insider, who will shake up government with fresh ideas and a new approach.

A portion of the Republican base, and especially Trump's base, revels in going after Bill Clinton for his past. But that tact is likely to obscure from the more fruitful attacks, on her family's charitable foundation and her use of a private email server during her tenure as secretary of state.

"It is generally a waste of time to re-litigate issues from the last century," a Republican consultant warned.