Kamala Harris has arrived in Chicago for the Democratic National Convention (DNC), where she will be formally confirmed as the party’s presidential candidate.
She flew into O’Hare airport on Air Force Two after a day of campaigning in the swing state of Pennsylvania with her running mate, Tim Walz.
Her Republican rival, Donald Trump, held a rally in Pennsylvania on Saturday.
Ms Harris is expected to join President Biden on stage when he addresses the convention on Monday.
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.
Ms Harris arrived in Chicago on Sunday ahead of the Democratic National Convention, where delegates will recognise her as the nominee for the 5 November election.
The convention will culminate on Thursday with Ms Harris giving a primetime speech after she formally accepts the party’s nomination.
Security around the venue is tight ahead of the four-day event, with tens of thousands of pro-Palestinian protesters expected to rally in Chicago.