Harris, the first woman and first Black and South Asian person to serve as vice president, has narrowed her list of candidates to Pennsylvania Governor Josh Shapiro and Minnesota Governor Tim Walz, sources told Reuters on Monday, after considering a field of finalists made up of white men with a record of winning over rural, white or independent voters.
A campaign official said no calls were being made about a choice on Monday night, suggesting Harris had not told her potential running mates who would get the job.
Harris became the Democratic Party's standard bearer after President Joe Biden ended his re-election campaign last month. Since then, she has raised hundreds of millions of dollars and recast the race against Republican Donald Trump with a boost of energy from her party's base.
Although she had gathered enough delegates to be her party's nominee, the Democratic National Committee said late on Monday that she had officially secured the nomination.
Harris is expected to appear with her running mate at an event in Philadelphia on Tuesday evening. Her selection will demonstrate her thinking about her best pathway to winning the presidency and show who she believes would serve as an effective governing partner should she prevail against Trump.
Shapiro, 51, is a rising star in the party with strong approval ratings in Pennsylvania, whose 19 electoral votes make it a must-win state for both Harris and Trump.
Walz, 60, serves as governor in a solidly Democratic state but has proven appeal to rural, white voters, who in recent years have voted broadly for Trump.
Americans typically focus on the person at the top of the ticket when choosing whom to vote for, but vice presidential candidates can help or hurt their running mates based on their backgrounds, home state popularity and ability to sway important constituencies or independent voters.
Trump's vice presidential pick, U.S. Senator JD Vance of Ohio, has had a rocky start since joining the Republican ticket, with old comments criticizing "childless cat ladies" drawing unwelcome attention and potentially alienating women voters.
Vance will follow Harris and her new running mate to several swing states this week, the Trump campaign said, including stops in South Philadelphia on Tuesday and Michigan and Wisconsin on Wednesday. He plans to criticize Harris on economic issues and immigration.