"My response is the president is not going to steal this election," Biden told reporters before leaving an event for Rep. Brendan Boyle's (D-Pa.) reelection campaign in Philadelphia.
Trump and Biden campaigned in Pennsylvania this weekend, with Trump holding four rallies in the Keystone State on Saturday and Biden headlining a number of events on Sunday.
The Democratic nominee is also set to spend all of Monday campaigning in the battleground state.
Pennsylvania's early count is likely to favor Trump because of state laws against counting mail-in ballots before Election Day.
Numerous polls show Biden leading the president in Pennsylvania.
The RealClearPolitics average shows Biden leading Trump by 4 points in the state.
Trump won the state by roughly a point in 2016, contributing to what was widely considered a surprise victory. »