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 increasing infrastructure spending.
Has run for president twice before.
Is among the best-liked figures in the Democratic Party, 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.
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Would be one of the most gifted orators in the field, running on a politics of uplift that could recall President Obama’s 2008 campaign.
Enjoys a vast fund-raising base, thanks to longstanding connections to donorsaround the country.
SIGNATURE ISSUES: Has been one of the leaders in the Senate on criminal justice reform, but his appeal would most likely center on his call to unify the country.
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 campaignthat 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 change and economic opportunity.
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.
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 health care.
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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.
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.
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.
SIGNATURE ISSUES: Unveiled middle-class tax cut legislation last fall, and has championed a liberal civil rights agenda in the Senate.
A political moderate with a record of success in a purple state.
A former geologist who struck it rich when he opened a brewery in Denver.
Will probably cast himself as someone who can attract support from a broad coalition, though some of his victories entailed cutting deals with the Republican business establishment.
SIGNATURE ISSUES: Has stressed his record of consensus-building around issues like expanding Medicaid, gay rights and gun control.
A two-term governor known for his environmental policies.
Has become one of the party’s most forceful climate advocates, calling on Democrats to embrace a green-energy jobs program.
SIGNATURE ISSUES: Has made climate a centerpiece of his agenda as governor and as a national figure, campaigning widely in the midterm elections on a message of creating renewable energy jobs.
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.
Defeated a long-time incumbent to become his city’s first black mayor.
Has taken progressive stances on guns, immigration and environmental issues.
A first-generation American born to Jamaican parents, he is hoping to tap into the Caribbean-American community to help fuel his long-shot bid.
SIGNATURE ISSUE: Has proposed canceling the more than $1.5 trillion in student debt owed by 44 million Americans.
Won his congressional seat in 2014 after ousting a longtime Democratic incumbent.
Has made his military service a key piece of his political brand.
Helped lead an effort to oppose electing Representative Nancy Pelosi speaker in the new Congress.
SIGNATURE ISSUES: Has stressed his four tours in Iraq with the Marine Corps and called for a new approach to foreign policy, national security and defense.
Has delivered a message of national unity and red-state liberalism via constant social media livestreaming to voters inside and outside Texas.
Any success in 2020 would draw from this viral appeal, particularly to younger Democrats, and from the small-dollar fund-raising army it has earned him.
SIGNATURE ISSUES: Has focused on immigration reform, marijuana legalization and rural hospital access.
Joined Congress at age 29 and has positioned himself as a voice for blue-collar voters in the Midwest.
Challenged Nancy Pelosi for House minority leader after the 2016 election, winning 63 votes to her 134.
Once an opponent of abortion rights, gradually reversed his position and announced in 2015 he considered abortion a “personal choice.”
SIGNATURE ISSUES: Renegotiating or enforcing trade deals; punishing Chinese currency manipulation; unions rights and workforce development.
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 in the Democratic primary.
Might face difficulties retaining the 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.”
Has a growing national profile, thanks to his popularity as a cable news guest.
As a member of the House Judiciary and Intelligence Committees, could have a high-profile presence on issues like impeachment and the Russia investigation.
SIGNATURE ISSUES: Has stressed his experience as a prosecutor to investigate the Trump administration; proposed funding for innovation in medical research; pushed for a national ban on assault weapons.
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.
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.
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.
Main legislative accomplishment as president: a sweeping tax cut that chiefly benefited corporations and wealthy investors.
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.
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.