Kamala Harris was set to announce her running mate Tuesday before the pair head out on a five-day swing through America’s hottest battleground states, just three months out from the presidential election.

The US vice president’s campaign has come out of the blocks at a lightning pace since she replaced Joe Biden at the top of the Democratic ticket, smashing fundraising records and wiping out the leads built up by Republican rival Donald Trump.

Pennsylvania Governor Josh Shapiro, a Democratic rising star, is considered the favorite to join Harris as her vice-presidential pick, ahead of several other state governors, a US senator and Transportation Secretary Pete Buttigieg.