Kamala Harris arrives in Chicago for Democratic National Convention

Pennsylvania has been a crucial battleground in recent presidential races, with Donald Trump winning the state in 2016 and Joe Biden in 2020.

A new CBS News poll shows Mr Trump and Ms Harris are neck and neck in the swing states of Pennsylvania, Michigan and Wisconsin.

In a speech on Sunday, Ms Harris indirectly criticised her opponent, suggesting he was a “coward” whose politics focused on putting down rivals.

“What we know is the real and true measure of the strength of a leader is based on who you lift up,” she told a crowd of supporters.

“Anybody who’s about beating down other people is a coward.”

A day earlier in the same state, Mr Trump called his Democratic rival a “lunatic” and bragged that he was “much better looking” than her.