The texts telling people to rally in Philadelphia were sent using phone numbers leased to the text-messaging platform Opn Sesame, owned by the Trump campaign's digital director.

Trump, who thrives on the energy from packed arenas, has not held a rally since March 2 in Charlotte, North Carolina.

With little more than five months left until the election, Trump is behind Democratic rival Joe Biden in national polls and in some battleground states, such as Michigan, which he won in 2016.