A single fingerprint taken from a mail bomb sent to Rep. Maxine Waters helped investigators get a break in solving a terror plot that targeted senior Democrats and vocal opponents of President Trump, federal officials said.

That clue led investigators on Friday to a white van parked outside an AutoZone shop in Plantation, Fla. The van was plastered with images of Mr. Trump and Vice President Mike Pence. It also had pictures of liberal figures in crosshairs.

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