The vice president told a crowd of roughly 20,000 in Dallas that former President Donald J. Trump had said he would terminate the Constitution in a second term.

“Consider: Donald Trump has openly vowed if re-elected he’ll be a dictator on day one, that he will weaponize the Department of Justice against his political enemies, round up peaceful protesters and throw them out of our country and even, and even and I quote, ‘terminate’ the United States Constitution,” Ms. Harris said.