The list of candidates to run with Kamala Harris, the presumptive Democratic U.S. presidential nominee, narrowed on Monday, with North Carolina Governor Roy Cooper and Michigan Governor Gretchen Whitmer both out.

The high-stakes decision has taken center-stage since Vice President Harris became the Democratic frontrunner for the November election just over a week ago after President Joe Biden ended his White House bid.

Vice presidential nominees can be used to balance a presidential candidate's ticket to appeal to a wider swath of voters, and Harris is weighing a list of mostly white, male candidates.

Cooper withdrew from Harris' vice presidential candidate pool, saying in a statement on Monday: "I was honored to be considered for this role. This just wasn't the right time for North Carolina and for me to potentially be on a national ticket."

Also on Monday, Whitmer said on "CBS Mornings" that she was "not a part of the vetting" process for Harris' running mate.

"I have communicated with everyone, including the people of Michigan, that I'm going to stay as governor until the end of my term at the end of 2026," Whitmer said.

Harris took a break from the campaign trail this weekend and held private conversations with several of the candidates, including Pennsylvania Governor Josh Shapiro, according to two sources familiar with the calls.

Others under consideration include Kentucky Governor Andy Beshear, U.S. Senator Mark Kelly of Arizona, Minnesota Governor Tim Walz, and Secretary of Transportation Pete Buttigieg.

Candidates have hit the national television circuit to showcase what they bring to the campaign.

Buttigieg, considered by even his allies as a long shot, talked to Harris privately about the opportunity, according to two sources familiar with the event.

He also held a call with a group of donors from his 2020 presidential bid where he said he wanted the job, but was going to respect the process, the sources said.