She has referred to him as a “moron.”

He has publicly expressed a desire to hit her with the oversized wooden gavel used to keep order in the House, aides later insisted.

Speaker Nancy Pelosi’s relationship with the man most likely to succeed her if Republicans win control of the House in next month’s elections is barely civil. And, as the potential succession date approaches, she has become less interested in hiding her disdain for top Republican Representative Kevin McCarthy of California.

At a news conference last week, when asked to respond to Mr. McCarthy’s claim that she was not allowing Democrats to speak out about what he described as a crisis at the border, Ms. Pelosi said of the minority leader, “I don’t even know what he’s talking about — and I don’t know if he does.”

The same week, her spokesman, Drew Hammill, chastised Mr. McCarthy for holding a press conference on the Capitol steps to discuss “firing Nancy Pelosi.” “About par for the course for an uninspiring and incoherent politician like the minority leader, whose only real accomplishment to date is typing up a radical right-wing wish list that sends a clear message to the American people that House Republicans have gone off the deep end,” Mr. Hammill said.

That was the final version.

Ms. Pelosi, who is now in her eighth year as the House’s first female speaker, specializes in emasculating male counterparts she finds lacking. During Trump’s presidency, she honed her craft.

Mr. McCarthy, 57, made his gavel remark in front of a group of donors last year, providing Ms. Pelosi with plenty of fodder for mockery and ill will. Mr. McCarthy said she had “broken this institution” when she barred Trump supporters from joining the select committee investigating the Capitol riot on January 6, 2021. He frequently refers to her as a “lame duck speaker.”

Mr. McCarthy, on the other hand, has accused her of partisanship and abuse of power, whereas Ms. Pelosi, who colleagues say despises spinelessness and stupidity, has accused him of acting like a buffoon.

Mr. McCarthy’s eight-and-a-half-hour floor speech last year, which at times veered into the nonsensical, delayed House passage of Democrats’ marquee domestic policy bill, and Ms. Pelosi’s office called it a “meandering rant,” adding, “As he hopefully approaches the end, we’re all left wondering: Does Kevin McCarthy know where he is right now?”

On Capitol Hill, partisan feuds and name-calling are nothing new. Former Speaker Tip O’Neill, a Democrat from Massachusetts, referred to three of his Republican adversaries as the “Three Stooges”: Representatives Newt Gingrich of Georgia, Bob Walker of Pennsylvania, and Vin Weber of Minnesota. However, Mr. Gingrich claims that the nickname was given “in good fun.”

In recent history, speakers — who are partisan leaders but are also elected by the entire House, as the Constitution requires — have shown at least a modicum of respect to their counterparts in the opposing party, as a nod to their institutional responsibilities.

Ms. Pelosi takes pride in her command of her fractious caucus and her ability to navigate complex and high-stakes legislation through the often-raucous House. Mr. McCarthy, who famously separated former President Donald J. Trump’s favorite red and pink Starburst candies from the rest of the pack and presented them to him to curry favor, has spent his congressional career focusing on politics rather than policy. In recent years, he has frequently catered to the most extreme members of his conference.

While she did not have a close relationship with the two Republican speakers who preceded her, John Boehner and Paul Ryan, their offices worked together on a regular basis, and Ms. Pelosi never held them in such low regard. Ms. Pelosi has almost no involvement with Mr. McCarthy’s office, even behind the scenes. This year, House Republicans did not participate in negotiations to keep the government funded.

Mr. McCarthy was elected to Congress from California’s Central Valley in 2007, the same year Ms. Pelosi became the first woman to be elected speaker. He did not rise to leadership until 2014, and Ms. Pelosi was gracious at the time about working opposite someone from a conservative wing of her home state.