NEW YORK — Roger Ailes, the former Fox News chairman ousted last month over charges of sexual harassment, is advising Donald Trump as he begins to prepare for the all-important presidential debates this fall.

Ailes is aiding Trump’s team as it turns its attention to the first debate with Hillary Clinton, the Democratic nominee, on Sept. 26 at Hofstra University on Long Island, N.Y., according to four people briefed on the move, who insisted on anonymity because they were not authorized to discuss the matter.

Two of them said that Ailes’s role could extend beyond the debates, which Trump’s advisers see as crucial to vaulting him back into strong contention for the presidency after a series of self-inflicted wounds that have eroded his standing in public opinion polls.

For Ailes, being connected with Trump’s campaign could be a form of redemption after he was pushed out of the powerful network that he helped build. And for Trump, having Ailes taking a hand in his preparations for the debates adds immeasurably to the messaging and media expertise in his corner — and could raise alarms within Clinton’s camp about just how aggressive Trump plans to be in those encounters.

It was not clear when Ailes began helping the campaign. He resigned from his post at Fox News on July 21 amid an investigation into allegations of sexual harassment by former female employees that occurred after a lawsuit by former anchor Gretchen Carlson.

It was also not immediately known whether Ailes, who received $40 million in an exit agreement with Fox News, will be paid for his work on the campaign, or how much time he will be devoting to it. Trump’s campaign chairman, Paul Manafort, is not being paid.

Susan Estrich, a lawyer who is representing Ailes, did not immediately respond to an e-mail­ inquiry and phone message Tuesday.

A spokeswoman for Trump, Hope Hicks, denied that Ailes was advising him in any capacity. Noting in an e-mail that “Mr. Ailes and Mr. Trump have been friends for many years,’’ she said their relationship was being mischaracterized.

“They speak occasionally, which isn’t news,’’ she said.

Before he founded Fox News in 1996, Ailes spent years as a respected political strategist with a pit-bull style. He was a top adviser to Richard M. Nixon’s presidential campaign in 1968, softening his hard-edge, unapproachable image.

He was also a sought-after debate coach, working with Ronald Reagan in 1984 and readying Vice President George Bush for debates with the Democratic candidate, Massachusetts governor Michael Dukakis, in 1988.

According to Gabriel Sherman’s 2014 book on Ailes, “The Loudest Voice in the Room,’’ he played a crucial role before Reagan’s second debate with former vice president Walter F. Mondale in 1984. During a prep session, he asked Reagan, who performed badly in the first debate, how he would handle being asked about his age.

The question came quickly, and Reagan’s answer, which went down in the annals of witty debate lines, effectively quashed the subject:

“I will not make age an issue of this campaign,’’ he said. “I am not going to exploit for political purposes my opponent’s youth and inexperience.’’

In 1988, Ailes was enlisted for an image makeover of George H.W. Bush, urging the patrician Republican to model himself after actor Gary Cooper. In debate prep, Ailes launched rapid questions at Bush to hone his reflexes, and directed the candidate to slow his sentences and deepen his voice, according to Sherman’s book.

Ailes also worked on lower-level political races including the unsuccessful New York City mayoral campaign of Rudy Giuliani in 1989. Giuliani has emerged as one of Trump’s most devoted surrogates in the presidential campaign.

Ailes and Trump themselves have a long relationship, although it became fraught at points during the GOP primaries.

Still, Ailes’s involvement is certain to stoke controversy, both for the ongoing sexual harassment cases and for the role that Fox News played in covering Trump’s candidacy — and elevating him as a potential presidential candidate beginning in 2011.

One of Trump’s longest-lived and highest-profile campaign controversies was a dispute with Fox News host Megyn Kelly, with whom he clashed angrily beginning with the first Republican primary debate a year ago. Afterward, Trump implied that she had been agitated during the first Republican debate because she was menstruating.

Trump insisted that Kelly had treated him unfairly and berated the network for suggesting that she moderate at a later debate. The dispute led Trump to skip the final debate before the Iowa caucuses, which Kelly moderated on Fox News.

Notably, when Ailes left the network in July, Manafort denied suggestions that Ailes would be joining the Trump campaign — but the candidate left the door open.