More than half of the record spending on negative advertising during the 2016 presidential primary has been directed at a single candidate, Donald J. Trump, a barrage that threatens to undermine his candidacy even as he continues to march toward the Republican nomination.
Of the more than $132 million spent on negative ads by candidates and the groups supporting them, nearly $70 million has gone to commercials assailing Mr. Trump, according to a New York Times analysis of data provided by Kantar Media/CMAG. The sharp focus on a single candidate is especially surprising given the exceptional size of the initial Republican field.
In addition to Mr. Trump’s opponents, three Republican “super PACs” have made it their main focus to take him down. The Club for Growth, Our Principles PAC and the American Future Fund, all unaligned with any particular candidate, have spent more than $23.5 million on negative ads against him.
On Monday, Hillary Clinton crossed primary lines to add to the onslaught, releasing a commercial that highlights comments Mr. Trump has made about immigration and abortion and argues that he is trying to get Americans to turn against one another.
“What is unusual and unprecedented is the array of advertisers who are out there flogging Trump on the air,” said Elizabeth Wilner, a senior vice president at Kantar Media/CMAG. “You have general election foes attacking him, you have his primary foes attacking him, and you have specific groups whose whole focus in life is just to make sure that he’s not the nominee.”
The amount of spending on negative and contrast ads, which are partly critical, against Mr. Trump is yet another example of the unique way in which he has dominated the Republican primary campaign so far. Largely because of his high name recognition and established brand, he has mostly withstood the attacks, building on his delegate lead and polling well in states that vote soon. In New York, which holds its primary next week, he has the support of more than 50 percent of likely Republican voters.
But despite claims that campaign advertising has lost its potency, there is growing evidence that negative ads still work — and that they are beginning to take their toll on Mr. Trump.
Ken Goldstein, a professor of politics at the University of San Francisco who tracks campaign advertising, pointed to Wisconsin as a place where the ads, paired with a focused message, a smaller field and a persuadable electorate, had an effect.
“Negative ads are never a silver bullet,” Mr. Goldstein said. “What negative ads in particular do is allow people to introduce or amplify messages that are out there with movable people.”
In Florida, by contrast, a large state with several media markets, Mr. Trump faced a significant amount of negative advertising from various groups, but the scattershot message failed to take hold, and he cruised to victory.
Beyond the primary battle, the surge of negative advertising could start to harm Mr. Trump’s general election prospects.
It started in earnest in December, when Right to Rise, a group supporting Jeb Bush, spent $2.1 million on an ad portraying Mr. Trump as a “bully.” At the time, Mr. Trump had relatively high unfavorable ratings compared with the other candidates: 57 percent among all Americans, according to a CNN/ORC poll from that month.
But as the ads began to increase in frequency and the tone turned more negative, his national unfavorable rating began to climb unabated. A CNN/ORC poll last month found that it was up 10 points from December, to 67 percent: 11 points higher than any other candidate still in the race, Republican or Democrat.
Mike Murphy, who was the chief strategist for Right to Rise, said the ads had kept Mr. Trump from consolidating more support in the Republican primary.
“I think the negative ads are having a chilling effect on his ability to grow his natural share with converts,” Mr. Murphy said. However, he added, Mr. Trump’s own mouth plays a role.
“He creates an environment where negative ads are a little more fertile,” Mr. Murphy said, adding that the ads were having more impact now that fewer candidates are in the primary race.
Larry McCarthy, a Republican strategist who worked with Mr. Murphy and now produces ads for Our Principles PAC, said his group had found, through polling and focus groups, that the best way to go after Mr. Trump was to use the bombastic billionaire’s own words against him.
“Campaigns use negative ads because they work,” said Ryan Williams, a Republican strategist and vocal critic of Mr. Trump. “And Donald Trump has provided his opponents with a bonanza of negative information to use in ads targeting his candidacy.”
Compounding the risks for Mr. Trump is that he has done little to counteract the effort with his own spending. He has spent just over $16 million on television ads, and in later contests, he went on the air late or not at all. A spokeswoman for Mr. Trump, Hope Hicks, did not respond to an email requesting comment.
Mr. Williams, who worked on Mitt Romney’s 2012 presidential campaign, recalled how allies of President Obama aired a devastating ad that eviscerated Mr. Romney’s character. It was paired with the Obama campaign’s own ads, which began running in the late spring and stayed on the air through the election.
Mr. Romney, who was still duking it out in his own primary campaign, did not start airing ads in earnest until the fall. By then, he was well defined in the public’s eye.
“President Obama’s super PAC ran an ad that basically accused Mitt Romney of giving a woman cancer,” Mr. Williams said. “The ads were outrageous, offensive and widely panned by the media and fact checkers. But unfortunately, with several million dollars behind them, they were effective in damaging his image.”
The enduring potency of negative ads has helped the Republican candidates define opponents other than Mr. Trump. In December and January, a super PAC supporting Senator Marco Rubio of Florida took aim at Gov. Chris Christie of New Jersey as Mr. Christie was making a late push in New Hampshire. The ads, which painted Mr. Christie as corrupt and too close to Mr. Obama, took a toll, and Mr. Christie, who wound up finishing sixth in New Hampshire, was forced from the race.
Right to Rise also used its advertising budget to reinforce negative perceptions about Mr. Rubio, which, coupled with a poor debate performance, halted his early rise.
But in those cases, the targets were easier: Neither Mr. Rubio nor Mr. Christie was particularly well known at a granular level among voters, so new information helped shape voters’ perceptions. Mr. Trump is an established brand for many people, which means that damaging his reputation is likely to require a more concentrated effort.
To that end, Priorities USA — the super PAC supporting Mrs. Clinton, which also backed Mr. Obama in 2012 — has begun reserving $70 million in television ad time from the Democratic convention in late July through Election Day, air time that is almost certain to be dedicated to ravaging Mr. Trump if he is the nominee.
Steve Murphy, a veteran Democratic ad maker, said that Mr. Trump should view the primaries as a mere taste of what is to come.
“Ask Donald Trump if he thinks negative ads hurt him in Wisconsin,” Mr. Murphy said. “Then tell him the Democrats have another half a billion dollars’ worth ready to go in the general.”