Kamala Harris is set to announce her running mate on Tuesday, just ahead of a five-day tour through key battleground states, as the presidential election draws closer.

Since taking over the Democratic ticket from Joe Biden, Harris's campaign has been rapidly gaining momentum, breaking fundraising records and narrowing the gap with her Republican opponent, Donald Trump.

Pennsylvania Governor Josh Shapiro is currently the frontrunner to join Harris as her vice-presidential candidate, with other contenders including Minnesota Governor Tim Walz, US Senator, and Transportation Secretary Pete Buttigieg. Reports suggest that Harris has narrowed her choice down to Shapiro and Walz, with an announcement expected soon.

Despite the anticipation, Harris has kept her decision under wraps, stating in a text message to supporters that she had not yet made her final decision.

Harris and her chosen running mate will kick off their campaign with a rally at Temple University in Philadelphia, followed by visits to Wisconsin, Michigan, Arizona, and Nevada. However, planned events in North Carolina and Georgia have been postponed due to a tropical storm affecting the southeastern states.

Shapiro's popularity in Pennsylvania, a crucial swing state, makes him a strong candidate, and his inclusion would add to the ticket's diversity, as he would be the first Jewish vice president. However, his stance on Israel has sparked some backlash from the left.

Walz, known for his rural Midwestern perspective and recent effective communication against Trump, is seen as another strong option from the liberal wing of the party.

Other potential candidates include Arizona Senator Mark Kelly, Kentucky Governor Andy Beshear, and Illinois Governor J.B. Pritzker.

Harris began her search for a running mate after Biden withdrew from the race on July 21, amidst concerns about his popularity and age, and as Trump surged following an assassination attempt and a strong performance at the Republican National Convention.

Recent polls indicate Harris's growing lead over Trump, though some caution that the race remains tight, particularly with Black voters, highlighting the challenging road ahead for both sides.