"You can't know if you can break through if you don't get out there and try," Patrick said. "I've been waiting for a moment like this my whole life. And by that I don't mean a moment to run for president, but a moment when the appetite for big ideas is big enough for the size of the challenges we face in America."

Proponents of Patrick’s campaign view him as the rare candidate who could unite the party’s progressive wing — currently represented in the primary by Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts — with the more moderate voters who remain largely committed to Joe Biden, despite doubts among the donor class regarding the viability of the former vice president’s candidacy.

He implicitly criticized them in his remarks Thursday.

"Right now, we have a really talented, really gifted, and a very hardworking and hard-sacrificing field of Democratic candidates, many of them my personal friends. But we seem to be migrating to, on the one camp, sort of nostalgia, let's just get rid, if you will, of the incumbent president and we can go back to doing what we used to do. Or, you know, it's our way, our big idea, or no way," Patrick said. "And neither of those, it seems to me, seizes the moment to pull the nation together and bring some humility that — frankly — we have a lot of ideas, but no one candidate, no one party has a corner on all the best ideas."

Skepticism about Biden‘s durability, as well as fears sparked by Warren’s ascendancy in public polling, has fueled calls by some center-left Democrats for a fresh candidacy in the nominating contest.

Patrick pitched himself Thursday morning as a more moderate choice than Warren or Sanders. Patrick said he supports a public health care option, but not the “Medicare for All” proposal that is popular with the party's left wing. He also said he's not opposed to a wealth tax, a key component of Warren's campaign, but called for simplifying the tax code more broadly.

"I don't think that wealth is the problem. I think greed is the problem," said Patrick, who joined the private equity firm Bain Capital after leaving office.

News of Patrick's presidential plans broke earlier this week. The decision to jump into the race marked a reversal for the former governor — he ruled out a run last December, citing the impact the “cruelty“ of the election process would have on his family.

Patrick faces an uphill climb to the Democratic nomination. The Iowa caucuses and New Hampshire primary are only a few months away. And he’s already missed deadlines to file for the primary ballot in Alabama and Arkansas. Those close to the ex-governor say he hopes to create momentum in New Hampshire and South Carolina, but a source familiar with Patrick’s plans acknowledged on Wednesday that the campaign could also falter early because of its late start.

Patrick made his campaign public with an announcement video online early Thursday morning saying the race for the White House is about “more than removing an unpopular and divisive leader."

He laid out a vision for reclaiming the American dream, saying he was given opportunities but sees the path closing off for others. His story is a powerful one: Patrick grew up poor in Chicago, received a scholarship to a prestigious Massachusetts prep school, graduated from Harvard Law School and became the second black governor in history.

Patrick was elected governor in 2006 and served two terms. He was an early backer of President Barack Obama in 2008, and served as a surrogate for Obama on the campaign trail in 2012 against another former Massachusetts governor — Republican Mitt Romney.

Natasha Korecki, Alex Thompson and Quint Forgey contributed to this report.