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.