Michael Bennet, 55
Senator from Colorado
“We cannot be the first generation to leave less to our kids, not more. That's why I'm running for president. Let's build opportunity for every American and restore integrity to our government.”
A moderate Democrat known for seeking compromise.
Is best known for being a part of the so-called Gang of Eight, a bipartisan group that crafted a comprehensive immigration reform bill in 2013.
Announced in early April that he had prostate cancer, but has since had surgery that his staff called “completely successful.”
Signature issues: Has called for modernizing the economy in fields like artificial intelligence and for increasing infrastructure spending.
Joseph R. Biden Jr., 77
Former vice president; former senator from Delaware
“If we give Donald Trump eight years in the White House, he will forever and fundamentally alter the character of this nation, who we are, and I cannot stand by and watch that happen.”
Has run for president twice before.
Is known for his down-to-earth personality and his ability to connect with working-class voters.
Regards 2020 as his last chance to run for president.
Signature issues: Restoring America’s standing on the global stage; strengthening economic protections for low-income workers in industries like manufacturing and fast food.
Michael R. Bloomberg, 77
Billionaire media executive; former mayor of New York City
“Defeating Donald Trump — and rebuilding America — is the most urgent and important fight of our lives. And I’m going all in.”
Recently reversed his longstanding support of the aggressive “stop-and-frisk” policing strategy that he pursued for a decade while he was mayor.
Has flirted with mounting a bid for president for more than a decade.
Re-registered as a Democrat in October, nearly two decades after he left the party to run for mayor as a Republican.
Has voiced stark disagreements with progressives on issues including bank regulation, stop-and-frisk police tactics and the #MeToo movement.
Signature issues: Has been an outspoken voice on gun control and climate change, but his views on taxes would put him on the conservative end of the Democratic field.
Cory Booker, 50
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.”
One of the most gifted orators in the field, is campaigning on the lofty ideals of love, unity and equality.
Has pitched himself as a healer in a political climate dominated by divisiveness.
Central to his campaign is combating inequality.
Signature issues: Has called for reversing mass incarceration with a sweeping clemency initiative, expanding affordable housing through tax credits and closing the racial wealth gap with his “baby bonds” proposal.
Pete Buttigieg, 37
Mayor of South Bend, Ind.; military veteran
“Running for office is an act of hope. You don’t do it unless you think the pulleys and levers of our government can be used and if necessary redesigned to make the life of this nation better for us all.”
Youngest candidate in the presidential field, says he would be a bridge to a new era of American politics.
Was the first candidate to push the idea of increasing the number of seats on the Supreme Court.
Has proven to be one of the most formidable fund-raisers in the race, collecting more money in the campaign’s second quarter than anyone else.
Signature issues: Has stressed his generational identity and focused on issues like climate change and economic opportunity.
Julián Castro, 45
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.”
Was a rising political star during the Obama administration but struggled to find a role afterward.
Opted out of challenging Senator Ted Cruz for the Senate in the 2018 midterm elections.
Delivered a standout performance in the first debate in June, declaring that the nation would soon say “adiós” to Mr. Trump.
Signature issues: Has called for overhauling the immigration system, including decriminalizing border crossings, and education policies like universal pre-kindergarten.
John Delaney, 56
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 visited every county in Iowa, but that hasn’t done much to improve his long-shot prospects.
Signature issues: Has pitched himself as a bipartisan problem-solver, but has also endorsed liberal causes like universal health care.
Tulsi Gabbard, 38
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.”
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.
Amy Klobuchar, 59
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, pitching herself as a pragmatist who can win there.
Signature issues: Has championed legislation to combat the opioid crisis and drug addiction, and to address the cost of prescription drugs.
Deval Patrick, 63
Former governor of Massachusetts; executive at Bain Capital, the private equity firm
“This time is about more than removing an unpopular and divisive leader, as important as that is, but about delivering instead for you.”
In 2006, became the second elected black governor in United States history.
A close friend of former President Barack Obama, has told advisers that he envisions a campaign focused more on bringing people together and healing the country than making a particular ideological case.
Signature issue: As governor, focused on economic development and innovation, and made Massachusetts a hub for life science jobs.
Bernie Sanders, 78
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, has brought progressive proposals like Medicare for All and tuition-free public college to the forefront of the race.
Was the runner-up in the 2016 Democratic primary.
Signature issues: “Medicare for all,” free college tuition and curtailing the influence of “the billionaires.”
Tom Steyer, 62
Billionaire former hedge fund executive; climate change and impeachment activist
“Americans are deeply disappointed and hurt by the way they’re treated by what they think is the power elite in Washington, D.C.”
Reversed a previous decision not to enter the race.
Started out as an environmental activist before airing millions of dollars in television ads demanding Mr. Trump's impeachment.
Has flirted repeatedly with running for statewide office in California.
Signature issues: Fighting climate change, promoting renewable energy and impeaching Mr. Trump.
Elizabeth Warren, 70
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.”
Speaks frequently about the need for “big, structural change.”
Has released a wide range of detailed plans that together have the potential to reshape the economy.
“I have a plan for that” has become her rallying cry and a T-shirt slogan.
Signature issues: Income inequality and what she sees as a middle class under attack from big corporations and political corruption.
Marianne Williamson, 67
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 a 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.”
Has based his campaign on a proposal to establish a universal basic income funded by the government.
Has drawn 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.
Donald J. Trump, 73
U.S. president; real estate developer; reality television star
“Considering that we have done more than any administration in the first two years, this should be easy. More great things now in the works!”
Main legislative accomplishment as president: a sweeping tax cut that chiefly benefited corporations and wealthy investors.
Has focused on undoing the policies of the Obama administration, including on health care, environmental regulation and immigration.
Faces multiple serious legal investigations, though the recent report by Robert S. Mueller III, the special counsel, found no evidence he coordinated with Russia’s 2016 election interference.
Signature issues: Restricting immigration and building a wall at the Mexican border; renegotiating or canceling international deals on trade, arms control and climate change; withdrawing American troops from overseas.
Joe Walsh, 57
Conservative radio show host; former congressman from Illinois
“We’ve got a guy in the White House who is unfit, completely unfit, to be president and it stuns me that nobody stepped up.”
Rode the Tea Party wave to Congress in 2010 and served one term in the House.
Staunchly supported Mr. Trump in 2016 “because he wasn’t Hillary Clinton,” but has since broken with the president.
Has called Mr. Obama a “Muslim” and a “traitor,” though he later said he regretted some of those comments.
Signature issues: Reducing the national debt; restraining executive power; securing the border; defeating Mr. Trump, who he says “can’t be trusted.”
William F. Weld, 74
Former governor of Massachusetts; former federal prosecutor
“I hope to see the Republican Party assume once again the mantle of being the party of Lincoln.”
Ran for vice president on the Libertarian Party ticket in 2016.
Is exploring a primary challenge to Mr. Trump, presenting himself as a voice for alienated moderates and mainstream conservatives.
Emerged as a vocal critic of Mr. Trump during the 2016 election, saying his call to deport immigrants evoked Kristallnacht.
Signature issues: Favors fiscal restraint, free trade and moderate immigration reform; has endorsed steps to legalize marijuana.