The pool of candidates to become the running mate of presumptive Democratic US presidential nominee Kamala Harris has narrowed, with North Carolina Governor Roy Cooper and Michigan Governor Gretchen Whitmer both out of the running.

The high-stakes decision has taken centre-stage since Vice-President Harris became the Democratic frontrunner for the November election just more than 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 swathe of voters.

Cooper withdrew from Harris’ vice-presidential candidate pool, a source familiar with his plans told Reuters on Monday.

His reasons for doing so were not immediately clear, although the Associated Press reported that he dropped out in part because of concerns his Republican lieutenant governor would assume control when he travelled out of state if he were selected..

The New York Times earlier reported Cooper’s withdrawal.

Also on Monday, Whitmer said on CBS Mornings she was “not a part of the vetting” process for Harris’s 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.

As well as Cooper and Whitmer, others who have been considered potential picks include Kentucky Governor Andy Beshear, US senator Mark Kelly of Arizona and Minnesota Governor Tim Walz.

– AAP