Harris’ campaign has sent vetting materials to North Carolina Gov. Roy Cooper, Pennsylvania Gov. Josh Shapiro, Arizona Sen. Mark Kelly, Michigan Gov. Gretchen Whitmer and Minnesota Gov. Tim Walz, all of whom have endorsed Harris to replace Biden, NBC News reported.

CBS says Harris’ team is vetting about a dozen people, including Kentucky Gov. Andy Beshear, Illinois Gov. J.B. Pritzker, Transportation Secretary Pete Buttigieg and Commerce Secretary Gina Raimondo in addition to the figures named by NBC.

Cooper and Harris have stumped for Biden in Cooper’s home state, which hasn’t picked a Democratic president since 2008 but is typically close, and he spoke to Harris over the phone Sunday, he told MSNBC on Monday.

Shapiro, who like Harris, previously served as his home state’s attorney general and fought lawsuits from former President Donald Trump and his allies challenging Biden’s 2020 win in the state, could help shore up support in a must-win Rust Belt state for Democrats.

Kelly also represents a swing state Biden narrowly won in 2020, and he defeated Trump-backed Republican Blake Masters in the 2022 midterm to help Democrats maintain control of the Senate—the former astronaut and husband of former Rep. Gabby Giffords, D-Ariz., tweeted Sunday he “couldn’t be more confident that [Harris] is the right person to defeat Donald Trump.”

Whitmer could also help the party win votes in a key swing state, but she said Monday she would not accept an offer to be Harris’ running mate.

Walz, who chairs the Democratic National Convention rules committee, told CBS Minneapolis affiliate WCCO on Monday becoming vice president is something he would “be a little nervous about.”

Kentucky’s popular governor, Beshear, who has won his deep-red state twice, is another potential pick for the No. 2 spot on a new Democratic ticket, though Democrats would still be unlikely to win Kentucky.

California Gov. Gavin Newsom, Colorado Gov. Jared Polis and Pritzker are other names commonly floated, but they could be at a disadvantage since they represent blue states, while Raimondo—who served as Rhode Island governor—is also reportedly under consideration.

Sen. Amy Klobuchar, D-Minn., and Buttigieg (who both endorsed Harris) are other potential candidates who have national name recognition from their 2020 presidential campaigns.

Sen. Raphael Warnock, D-Ga., if chosen, could also draw Black voters in the key swing state, where he’s proven he can beat Republicans—twice—in closely contested races, but if he leaves the Senate, his state’s Republican governor would pick his successor.

Maryland Gov. Wes Moore is another rising star in the Democratic party, but he said Monday he has “no intention” of leaving his current role.