US President Donald Trump and his predecessor, Barack Obama, have directed blistering barbs at each other during rival rallies.
Stumping in Pennsylvania for Democratic White House nominee Joe Biden, Mr Obama likened Mr Trump to a "crazy uncle" and said he gives succour to racists.
In North Carolina, the Republican president mocked Mr Obama for being wrong about the 2016 election outcome.
With 13 days to go until this election, Mr Biden holds a solid lead nationally.
But the margin is slimmer in the handful of US states that could go either way and ultimately decide the outcome on 3 November.
Americans are voting early at a record pace this year, with 42 million having already cast ballots both by post and in person.