Trump had been scheduled to speak in Virginia Beach.
De Blasio's cap featured the motto "Make America Fair Again."
The last poll showed the Democrat ahead by only 5 percentage points.
The conservative group hit the Ohio governor over Medicaid expansion.
Bush said it's "not known" whether Rubio has the skills to lead the country.
“That’s the biggest tragedy of the race," he said.
“Now if I tank, you know, sure. I go back to the business. Why wouldn’t I?" he says.
The vice president may be delaying his decision on the 2016 race.
“I bet you it’s not just the Russians,” he said of sources trying to access Clinton's server.
"They hate each other," Trump said.