Michigan Gov. Gretchen Whitmer delivers her State of the State address Jan. 24 at the state Capitol in Lansing, Mich. Al Goldis/Associated Press

President Biden on Sunday ended his reelection bid against former President Donald Trump and threw his support behind Vice President Kamala Harris.

The unprecedented move upended the presidential race less than four months before the election. If Harris becomes the Democratic nominee at the party’s convention in August – which is far from a sure thing – it’s not yet clear who her running mate would be, but here are some of the contenders:

GOV. ANDY BESHEAR

Public policy runs in the blood of Kentucky Gov. Andy Beshear. His father, Steve Beshear, served two terms as state governor. Before his tenure as governor, Andy Beshear, 46, served as the state’s attorney general from 2016 to 2019. The Kentucky governor recently reiterated his support for President Biden.

GOV. ROY COOPER

North Carolina Gov. Roy Cooper has also been mentioned as a potential running mate. Cooper, 67, served four terms as the state’s attorney general before his tenure as state governor. The lifelong North Carolina resident also served as a state representative and state senator. Cooper publicly stated his support for Biden’s run for a second presidential term.

SEN. MARK KELLY

U.S. Sen. Mark Kelly of Arizona, 60, backed the Biden-Harris ticket, as pressure for Biden to step aside continued to grow. Before Kelly made his way to Capitol Hill, representing a key swing state, he was a captain in the U.S. Navy and a NASA astronaut. Kelly is married to former U.S. Rep. Gabby Giffords, who survived a shooting in 2011 while meeting with constituents in Tucson, Arizona.

GOV. GAVIN NEWSOM

California Gov. Gavin Newsom, 56, is serving his second term as governor. Before winning over Californians for a second term in a recall election, he served as San Francisco mayor and as lieutenant governor. The progressive governor had reiterated his support for the president in the wake of Biden’s debate performance in Atlanta.

GOV. JOSH SHAPIRO

Pennsylvania Gov. Josh Shapiro, 51, gained attention for his swift response and public communication following the attempted assassination of former President Donald Trump. But Shapiro’s track record goes beyond the shooting in Butler, Pennsylvania. Shapiro, the governor of a key swing state, grew up in Pennsylvania and started his career as a political rookie, working his way up the ladder to governor.

GOV. GRETCHEN WHITMER

As governor of a swing state and co-chair of the Biden campaign, Michigan Gov. Gretchen Whitmer, 52, continued to support Biden while acknowledging concerns over the president’s mental acuity. Before being elected governor, Whitmer served as a state representative and state senator. She was elected to the Michigan State Senate in 2006 where she served as the Senate Democratic leader.