A few percentage points of difference in turnout by gender or education can produce very different results, both in election polls and in elections themselves.
With President Joe Biden out of the race, Democrats have started questioning the mental fitness of Trump, who would be the oldest president in history if he wins in November.
The former president's recent trashing of Detroit continues a long-running theme, and where Democrats see a cruel attack, Republicans see a play for suburban and rural voters.
Harris' campaign is ramping up outreach to the typically Democratic voting group, as polling suggests Trump could overperform among young men of all races.
The Justice Department said the Secret Service and the FBI are investigating. A law enforcement source said the matter wasn't seen as an assassination attempt.