Mr. Trump had previously turned to the women in his life to help counter claims that he is a misogynist. He frequently invokes Melania and his daughter, Ivanka, on the campaign trail, talking about how, behind the scenes, they are the ones urging him to behave “more presidential.”

“Again, my wife: ‘Darling, you’re so brilliant, you’re so bright. Act presidential. It’s so easy for you,’ ” Mr. Trump told a crowd Sunday night in West Allis, Wis., mimicking his wife’s breathy, accented voice. “I said, ‘Darling, I’ve got to win first, you know? I’ve got to win.’ ”

The decision to enlist Mrs. Trump comes as he has stumbled in recent weeks on issues that could damage him further with women, especially in a general election matchup against Hillary Clinton, who is trying to become the first female president.

Last week, in an interview with Chris Matthews of MSNBC, Mr. Trump said that should abortion become illegal, women who underwent the procedure should face “some form of punishment” — a view that put him at odds even with many fervent abortion opponents — before later recanting.

Candidate spouses are often deployed as character witnesses, and the Trump operation believes that Melania Trump, 45, could help her husband as he has faced a barrage of unflattering news reports. She first made an appearance on the campaign trail in February in South Carolina, at a time when Mr. Trump was in need of some image softening amid criticism of his combative rhetoric.

“She’s exceptionally smart, very articulate,” said Corey Lewandowski, Mr. Trump’s campaign manager. “She’s a great asset to the campaign.”