Senator Elizabeth Warren, a Democrat from Massachusetts, left, looks on as U.S. Secretary of State Hillary Clinton speaks during a Senate Foreign Relations Committee nomination hearing in Washington, D.C. on Jan. 24, 2013. Bloomberg/Getty Images Elizabeth Warren Elizabeth Warren is a firebrand populist senator from Massachusetts who has been vocally anti-Trump during the election. In June, Clinton said Warren would be " qualified " to be Vice President, and her campaign hasn't ruled out a female running mate.

Sen. Tim Kaine gives a 'thumbs-up' as he takes his seat at the head table for the National Prayer Breakfast in Washington, D.C. on Feb. 4, 2016. Pablo Martinez Monsivais—AP Tim Kaine Tim Kaine is a senator from the key swing state of Virginia who speaks Spanish and was a finalist for Barack Obama's vice presidential pick eight years ago. Reports say Kaine is now near the top of Clinton's list.

Democratic presidential candidate Hillary Rodham Clinton, right, with Housing and Urban Development Secretary Julian Castro, left, during a campaign event in San Antonio on Oct. 15, 2015. Eric Gay—AP Julian Castro Julian Castro is the United States Secretary of Housing and Urban Development and was formerly the mayor of San Antonio, Texas. Castro does not have as much political experience as other potential candidates, but his youth and Latino heritage could make him an attractive pick for Clinton.

Democratic presidential candidate Hillary Clinton laughs as U.S. Secretary of Labor Tom Perez endorses her during a campaign stop in Sioux City, Iowa, on Dec. 4, 2015. Nati Harnik—AP Tom Perez Tom Perez is the current United States Secretary of Labor. He does not have much experience in elected office, but Clinton may be considering him for his progressive bona fides and relationships with unions.

Democratic presidential candidate Hillary Clinton waves to supporters as she stands on stage with Sen. Sherrod Brown after speaking at a rally at a warehouse in Cleveland on June 13, 2016. Andrew Harnik—AP Sherrod Brown Sherrod Brown is a senator from the key swing state Ohio. Clinton praised brown during an economic speech in Columbus, and he introduced her at an event in Cleveland.

Democratic presidential candidate Hillary Clinton (C) is greeted by House Democratic Caucus Chair Xavier Becerra as she arrives to meet with House Democrats on Capitol Hill in Washington, D.C. on June 22, 2016. Alex Wong—Getty Images Xavier Becerra Xavier Becerra is a U.S. representative from California and the chairman of the House Democratic Caucus.

Democratic presidential candidate Hillary Clinton talks with Sen. Cory Booker at Omar's Cafe while campaigning, , in Newark on June 1, 2016. Julio Cortez—AP Cory Booker Cory Booker is a senator from New Jersey. The rising star in the Democratic Party has an active social media presence and stumped for Clinton during the primary.

Democratic presidential candidate former Secretary of State Hillary Clinton talks with Los Angeles mayor Eric Garcetti during a roundtable discussion at the University of Southern California in Los Angeles, on March 24, 2016. Justin Sullivan—Getty Images Eric Garcetti Eric Garcetti is the mayor of Los Angeles. He was floated as a possible vice presidential pick for Clinton and he campaigned for her during the California primary, but he recently told a radio station , "I’m not looking for a new job. I have a great one right now, and that’s being mayor of the city."

Rep. Tim Ryan raises his beer to toast Democratic presidential candidate Hillary Clinton at a packed O'Donold's Irish Pub and Grill in Youngstown, Ohio, on March 12, 2016. Carolyn Kaster—AP Tim Ryan Tim Ryan is a U.S. representative from the swing state of Ohio. He recently helped organize the House sit-in on gun control.

U.S. Senator Claire McCaskill introduces Democratic Presidential candidate Hillary Clinton prior to speaking during a campaign event at the International Association of Sheet Metal, Air, Rail and Transportation Workers in St. Louis, on Dec. 11, 2015. Michael B. Thomas—AFP/Getty Images Claire McCaskill Claire McCaskill is a senator from Missouri and has been a vocal supporter of Clinton during the primary.

Sen. Amy Klobuchar speaks at a Women Senators Endorsement Event for Democratic Presidential Candidate Hillary Clinton at the Hyatt Regency on Capitol Hill, in Washington, D.C. on Nov. 30, 2015. Congressional Quarterly/AP Amy Klobuchar Amy Klobuchar is a senator from Minnesota and has been an active surrogate for Clinton this election cycle, in what she called " the sisterhood of the traveling pantsuits ."

Democratic presidential candidate former Secretary of State Hillary Clinton dances with U.S. Sen. Jeanne Shaheen (center) and Lilly Ledbetter during a canvas kickoff event at the YWCA of Manchester in Manchester, New Hampshire on Feb. 5, 2016. Justin Sullivan—Getty Images Jeanne Shaheen Jeanne Shaheen is a senator from New Hampshire who campaigned for Clinton in her state and touted the candidate's foreign policy experience.