Former Colorado governor John Hickenlooper has announced his 2020 presidential bid.
The Democrat made the statement in a tweet, saying the country was "in crisis" and needed someone to "bring people together".
The post was accompanied by a video in which Mr Hickenlooper relates how he has stood up to his "fair share of bullies" during his career.
Mr Hickenlooper joins 14 other Democrats running for the top job.
He is the second governor to enter the field, following Washington's Jay Inslee who announced his bid last week.
US political analysts say he is sorely lacking name recognition among voters in an already crowded Democratic field, which includes US senators Bernie Sanders, Kamala Harris, Elizabeth Warren, Cory Booker, Amy Klobuchar and Kirsten Gillibrand.
Washington state Governor Jay Inslee, Congresswoman Tulsi Gabbard and Julian Castro, the housing secretary under the Obama administration, are also running.
The art of the possible
John Hickenlooper's presidential pitch to Democrats is simple. He's a practical businessman-turned-politician who has shown he can successfully enact progressive policies in a moderate state.
He points to his recently concluded two terms as governor of Colorado, where he presided over new environmental regulations (although he maintained his ties to the energy industry), the expansion of health care coverage (although he opposed a universal coverage proposal) and new gun-control laws (although his support was initially tepid).
In a field where many candidates are offering shoot-for-the-moon agendas, Mr Hickenlooper embraces politics as the art of the possible, noting that his success in Colorado came through good-faith negotiations and bipartisan compromise.
It's not an unheard-of strategy. George W Bush rode a-uniter-not-a-divider rhetoric to the White House in 2000. Barack Obama first captured the national spotlight in 2004, when he denounced a red state/blue state us-against-them outlook.
That may be a tougher sell this time around, however. Mr Hickenlooper will start toward the back of the pack, where only the loudest voices break through.
He's the second governor to enter the race, but Jay Inslee - who announced last week - is counting on his laser-like focus on climate change to distinguish his candidacy. Mr Hickenlooper is taking a broader approach, pitching himself to the majority of Democrats who say their top priority is someone who can beat Donald Trump.
The low-key, affable former brewpub-owner might be able to do that - but he's got an uphill climb if he wants to get the chance.
Who is John Hickenlooper?
Mr Hickenlooper, 67, worked as a geologist before he was laid off and founded a brewpub chain in Denver. He then served as the city's mayor from 2003-2011 and went on to serve as governor from 2011 to January 2019.
His video, titled "Stand Tall", features the Rocky Mountain and touts his record in office and in the private sector.
"We beat the NRA," he says, describing gun control legislation that requires universal background checks on gun purchases, and bans on high ammunition-capacity magazines in Colorado.
Former Colorado Gov. John Hickenlooper is running for President. Here’s his campaign logo. pic.twitter.com/HKBXojAdo7— Daniel Strauss (@DanielStrauss4) March 4, 2019
The legislation came after a mass shooting at a movie theatre in the state "that once again tore the heart of our community," he says in his video, adding that "just offering thoughts and prayers would never again be sufficient".
Describing himself as a "doer", he says he brought together the oil and gas industry and environmentalists to create new methane emissions in the swing state.
He also says he convinced Democrats and Republicans to work together to expand the state's Medicaid health care programme that has achieved coverage for nearly 95% of all residents.
It's official: I'm asking you to interview me for President. Our country is in crisis, and we need someone who knows how to bring people together and get things done. This is my record, but I've never done it alone. Join me: https://t.co/ta7aY0lTeY pic.twitter.com/HaCnK5paBU— John Hickenlooper (@Hickenlooper) March 4, 2019
Speaking on ABC News on Monday, he said America is in "the worst period of division we've had in this country since the Civil War".
Asked how he plans to stand out in a growing field of Democratic challengers, he said: "I think I'm really the one candidate out there that has a very strong record of bringing people together and getting things done."
"One thing I've shown I can do again and again is create teams of amazingly talented people and really address these critical issues that are facing the country."
He plans to hold his first rally on Thursday in Denver.
Also on Monday, former attorney general Eric Holder announced that he would not seek the presidency, but would support the Democratic field.
Mr Holder, who was attorney general under ex-president Barack Obama, said that after travelling to 25 states in the past year he "found that the people of this country are better, and more caring, than these small-minded leaders would have us believe".
Who will take on Trump in 2020?
John Hickenlooper has joined the race to stop Donald Trump from being re-elected. But who else has a shot at becoming the next president?