Cory Booker, 49

Senator from New Jersey; former mayor of Newark

“I believe that we can build a country where no one is forgotten, no one is left behind … where we see the faces of our leaders on television and feel pride, not shame.”

Would be one of the most gifted orators in the field, likely running on a politics of uplift that recalls President Obama’s 2008 campaign.

Enjoys a vast fund-raising base, thanks to longstanding connections to donors around the country.

Signature issues: Has been one of the leaders in the Senate on criminal justice reform, but his appeal would likely center on his call to unify the country.

Pete Buttigieg, 37

Mayor of South Bend, Ind.; military veteran

“I launched a presidential exploratory committee because it is a season for boldness and it is time to focus on the future.”

Began to draw national notice after delivering an essay that counseled Democrats on how to recover from their defeats in the 2016 elections.

Has embarked on a long-shot campaign that may test the appeal of a youthful profile over more traditional qualifications.

Signature issues: Has stressed his generational identity and called for policies on issues like climate and economic opportunity.

Julián Castro, 44

Former housing secretary; former mayor of San Antonio

“I’m running for president because it’s time for new leadership. Because it’s time for new energy.”

Opted out of challenging Senator Ted Cruz for the Senate in the 2018 midterm elections.

Once a rising political star, has struggled to find a role during the Trump administration.

Money could be an issue, especially if former Representative Beto O’Rourke, a small donor magnet, also mounts a bid.

Signature issues: Has emphasized a platform of universal prekindergarten, “Medicare for all” and immigration reform.

John Delaney, 55

Former congressman from Maryland; former businessman

“I think I’m the right person for the job, but not enough people knew who I was or still know who I am.”

Was elected to the House in 2012 as a “pragmatic idealist,” in his telling.

Has already visited every county in Iowa, though it’s unclear if he has improved his long-shot prospects.

Signature issues: Has pitched himself as a bipartisan problem-solver, but has also endorsed liberal causes like universal healthcare.

Tulsi Gabbard, 37

Congresswoman from Hawaii; Army National Guard veteran

“There are a lot of challenges that are facing the American people that I’m concerned about and that I want to help solve.”

Supported Bernie Sanders in the 2016 primaries.

Has drawn condemnation for meeting with Syria’s president, Bashar al-Assad, whose regime has been accused of using chemical weapons against civilians.

Has apologized for her history of anti-gay statements and her past work for an anti-gay advocacy group.

Signature issue: Opposition to American military intervention overseas, including in countries like Syria.

Kirsten Gillibrand, 52

Senator from New York; former congresswoman

“I’m going to run for president of the United States because as a young mom I am going to fight for other people’s kids as hard as I would fight for my own.”

Was once a congresswoman from a conservative House district (with policy positions to match).

Has transformed herself into a progressive champion in President Trump’s Washington, becoming one of the Senate’s leading liberal voices.

Signature issue: Has long placed women’s equality and opportunity at the center of her policy agenda.

Kamala Harris, 54

Senator from California; former attorney general of California; former San Francisco district attorney

“I believe our country wants and needs some leadership that provides a vision of the country in which everyone could see themselves.”

Would bring a star power and history-making potential to the race that few other Democrats can match.

One of few new Democrats to join the Senate after 2016.

Quickly drew notice for her tough questioning of President Trump’s cabinet nominees — and later, his Supreme Court nominee, Brett M. Kavanaugh.

Signature issues: Unveiled middle-class tax cut legislation last fall, and has championed a liberal civil-rights agenda in the Senate.

Amy Klobuchar, 58

Senator from Minnesota; former Hennepin County, Minn., attorney

“It is time to organize, time to galvanize, time to take back our democracy.”

Became a hero to many Democrats for her stern, cool questioning of Brett M. Kavanaugh during his confirmation hearings.

Has called for Democrats to focus on reclaiming the swing states in the middle of the country.

Signature issues: Has championed legislation to combat the opioid crisis and drug addiction, and to address the cost of prescription drugs.

Bernie Sanders, 77

Senator from Vermont; former congressman

“The only way we will win this election and create a government and economy that work for all is with a grassroots movement — the likes of which has never been seen in American history.”

A self-described democratic socialist.

Was the runner-up in the 2016 Democratic primary.

Would begin a second White House race with a more extensive organization-in-waiting than any other candidate.

Might face difficulties retaining the same level of support he enjoyed in what was effectively a head-to-head race against Hillary Clinton.

Signature issues: “Medicare for All,” free college tuition and curtailing the influence of, as he calls them, “the billionaires.”

Elizabeth Warren, 69

Senator from Massachusetts; former Harvard professor

“It’s time for women to go to Washington and fix our broken government, and that includes a woman at the top.”

Has done some of the most extensive preparations for a presidential run.

Attempted to dispatch questions about her Native American heritage by releasing the results of a DNA test.

That effort raised questions about her readiness for a national bid.

Signature issues: Income inequality and what she sees as a middle class under attack from big corporations and political corruption.

Marianne Williamson, 66

Self-help author, new age lecturer

“We need a moral and spiritual awakening in the country … Nothing short of that is adequate to fundamentally change the patterns of our political dysfunction.”

The author of more than dozen self-help and spirituality books.

Ran for Congress as an independent in 2014, and lost.

Championed the rights of gay men with AIDS, founding a charity that now supplies meals to people with serious illnesses.

Signature issues: Has proposed $100 billion in reparations for slavery, with $10 billion to be distributed annually over a decade for economic and education projects.

Andrew Yang, 44

Former tech executive who founded an economic development nonprofit

“Universal basic income is an old idea, but it’s an old idea that right now is uniquely relevant because of what we’re experiencing in society.”

Is running a long-shot campaign on a proposal to establish a universal basic income funded by the government.

Has drawn some media attention for highlighting tech issues like robotics and artificial intelligence.

Signature issue: Establishing a universal basic income of $1,000 per month for all Americans.