When Vice President Kamala Harris visited the southern border on Friday, she called fentanyl a “scourge on our country” and said that as president she would “make it a top priority to disrupt the flow of fentanyl coming into the United States.”

Ms. Harris pledged to give more resources to law enforcement officials on the front lines, including additional personnel and machines that can detect fentanyl in vehicles. And she said she would take aim at the “global fentanyl supply chain,” vowing to “double the resources for the Department of Justice to extradite and prosecute transnational criminal organizations and the cartels.”

But that was not how her opponent, former President Donald J. Trump, characterized her position on Sunday at a rally in Erie, Pa., where he made a false accusation against Ms. Harris that seemed intended to play on the fears and traumas of voters in communities that have been ravaged by fentanyl.

“She even wants to legalize fentanyl,” Mr. Trump said during a speech that stretched for 109 minutes. It was the second straight day that Mr. Trump had amplified the same false claim about Ms. Harris; he did so on Saturday in Wisconsin.

The former president did not offer context for his remarks, but his campaign pointed to an American Civil Liberties Union questionnaire that Ms. Harris had filled out in 2019 during her unsuccessful candidacy for the Democratic presidential nomination.

A question asking if Ms. Harris supported the decriminalization at the federal level of all drug possession for personal use appeared to be checked “yes.” Ms. Harris wrote that it was “long past time that we changed our outdated and discriminatory criminalization of marijuana” and said that she favored treating drug addiction as a public health issue, focusing on rehabilitation instead of incarceration.

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