Martin O'Malley, the liberal, former governor of Maryland, announced his bid Saturday for the Democratic Party's 2016 presidential nomination.
O'Malley, 52, faces formidable odds in opposing the front-runner for the nomination, former Secretary of State Hillary Clinton, 67.
O'Malley hopes that his successful effort to legalize gay marriage in Maryland, end the state's death penalty and raise its minimum wage for low-income workers will excite party voters.
He has made frequent forays into Iowa and New Hampshire, two states with early 2016 presidential nominating contests, and sometimes strummed an acoustic guitar at political rallies.
But so far O'Malley has attracted little political support, with one national poll this week showing him with just 1 percent Democratic support, far behind Clinton's 57 percent.
O'Malley served eight years as Maryland's top elected official and made his campaign announcement in Baltimore, the state's biggest city, where he was a two-term mayor before his statewide election as governor.
Baltimore was at the center of U.S. attention in April as rioting and looting erupted in an impoverished neighborhood in the aftermath of the death of a black suspect while in police custody. Six police officers have been charged with criminal offenses for their role in the suspect's arrest.
The disturbances also focused attention on O'Malley's tenure as mayor, when he advocated "zero-tolerance" tactics against lawbreakers to reduce crime, a policy that strained relations between the city's poor communities and police.
O'Malley has defended his work to curb crime, saying he helped address rampant violence and drug abuse. He has said the unrest in Baltimore should wake up the nation to the need to address despair in poor communities.
Already in the race is U.S. Senator Bernie Sanders, who could be O'Malley's main rival for the support of the Democratic left.
Also expected to join the Democratic race soon: former Rhode Island Governor Lincoln Chafee, who plans to make an announcement next week, and former U.S. Senator Jim Webb, who is exploring a potential campaign.
Crowded Republican field
On Thursday, former New York Governor George Pataki announced his candidacy for the Republican Party's presidential nomination.
Pataki, who led the state of New York during the September 11, 2001 terror attacks, kicked off his bid in a YouTube video, vowing a tough response to radical Islamists.
"I saw up close the horrible consequences of too many believing that because radical Islam was thousands of miles away across an ocean that we were safe in America. Sadly it wasn't true then and it's not true now," he said.
The 69-year-old Pataki, who has centrist political leanings, is seen as a long shot in a Republican field that already includes eight declared candidates, as well as eight others considering a run.
There are no front-runners in the 2016 Republican presidential primary, according to a Thursday poll by Quinnipiac University.
Leading the way with 10 percent each were former Florida Governor Jeb Bush, retired neurosurgeon Ben Carson, former Arkansas Governor and Baptist minister Mike Huckabee, Senator Marco Rubio, and Wisconsin Governor Scott Walker.
"With no front-runner and identical numbers for the top five contenders, it's a horse race which can only be described as a scrambled field - at least so far," said Tim Malloy, assistant director of the Quinnipiac poll.
Some material for this report came from AP.