Former President Donald J. Trump on Tuesday fired off a new attack against Representative Debbie Dingell, the widow of John D. Dingell Jr., the longest-serving member of Congress in American history, calling her a “loser” and suggesting that she had not been grateful for funeral honors granted by Mr. Trump for her husband.

The salvo from Mr. Trump, the Republican front-runner in the 2024 presidential race, followed an appearance by Ms. Dingell, a Democrat from Michigan, on CNN earlier on Tuesday in which she criticized Mr. Trump’s increasingly incendiary language on social media.

Weeks before the first nominating contests are held in Iowa and New Hampshire, the former president has amplified his vitriol. He shared a word cloud this week that prominently featured the word “dictatorship” and recently described people who entered the United States illegally as “poisoning the blood of our country,” comments that were condemned for being similar to the words of Adolf Hitler.

Ms. Dingell had been reacting to a grievance-filled Christmas message on Truth Social from Mr. Trump. Referring to his political opponents as “deranged” and “thugs” and accusing them of trying to destroy the country, he wrote, “MAY THEY ROT IN HELL. AGAIN, MERRY CHRISTMAS!”

The congresswoman — whom Mr. Trump has held a grudge against for years, implying in 2019 that her recently deceased husband was “looking up” from hell — said that it was another example of the former president fomenting anger.

“I think it was one of the most pathetic Christmas greetings I’ve heard when a former president of the United States who wants to return tells people on Christmas Day that they can rot in hell,” she told CNN. “He is contributing to the divisiveness and division in this country.”

Ms. Dingell’s criticism appeared to gnaw at Mr. Trump, who has long been preoccupied with her, starting with her 2019 vote to impeach him for the first time. About nine hours after her appearance on CNN, Mr. Trump targeted Ms. Dingell on Truth Social, saying that she had become an enabler of President Biden and his failed policies.

Mr. Trump returned to a familiar line of attack: the death of her husband in 2019 and his funeral honors.

“When I gave, as President, her long serving husband, the absolute highest U.S. honors for his funeral, a really big deal, she called me, crying almost uncontrollably, to say that she couldn’t believe I was willing to do that for a Democrat,” Mr. Trump wrote. “She thanked me profusely. Two months later, she was back on the trail ranting and raving about ‘TRUMP.’”

At the time, Mr. Trump had ordered American flags lowered to half-staff. He called Ms. Dingell to offer his condolences, but their accounts of that exchange diverge widely, with Mr. Trump repeatedly suggesting that he had played an outsize role in the “A-plus treatment” that was given to Ms. Dingell’s husband of 38 years.

Mr. Dingell retired from Congress in 2014 after serving his district, just outside Detroit, for 59 years. Ms. Dingell ran to succeed her husband and has been elected five times. Her 2019 vote to impeach Mr. Trump prompted anger from the president, who made headlines with the remark suggesting her late husband was in hell.

At a rally that year in Michigan, Mr. Trump mocked Ms. Dingell for the way he said she had conducted herself during the telephone conversation after her husband’s death. He suggested that Ms. Dingell had begged for him to lower American flags to half-staff and, apparently impersonating her, said: “Do this, do that, do that. Rotunda.”

Mr. Dingell did not lie in state in the Capitol Rotunda. Ms. Dingell has said that was not one of her husband’s requests.

On Tuesday, she excoriated Mr. Trump, telling CNN that his attacks had put her in danger.

“After he went after me, quite frankly, there were men outside of my house with assault weapons, and I have had threats,” she said.