In the closing stretch of the election, former President Donald Trump continues to emphasize claims of “migrant crime.” On Friday, he spoke in Aurora, Colorado, a city he charges is overrun by a Venezuelan gang. The Republican mayor has said such concerns have been “grossly exaggerated.” Immigration is a top voter concern, polls show, and Mr. Trump has doubled down on assertions that unauthorized-migrant criminals are endangering U.S. citizens. He’s also raised the profile of...