A formal announcement was delayed as the country observed a day of mourning for President George H.W. Bush, one source said. News of Patrick's plans was first reported by Politico.
Patrick, 62, served two terms as governor, from 2007 to 2015, was assistant attorney general for civil rights in the Clinton administration and since leaving the governor's office has been a managing director for Bain Capital. Patrick traveled the country in support of Democratic candidates in the recent midterm elections.
Earlier this year, some of Patrick's supporters and close advisers started the Reason to Believe political action committee, "a grassroots organization dedicated to advancing a positive, progressive vision for our nation in 2018 and 2020." Reason to Believe PAC had been holding meetups across the country, including in early presidential primary states.
While Patrick is opting against a 2020 run, dozens of Democrats are considering jumping in, including nearly a half-dozen members of the Senate, several House members, and other Massachusetts politicians. On Tuesday, Michael Avenatti, the attorney for adult film star Stormy Daniels and a vocal critic of President Donald Trump, said in a statement that he would not run.
Patrick had previously expressed some concerns about breaking through if he sought the nomination, telling David Axelrod, a former adviser to Barack Obama, that he wasn't sure he could stand out in such a large field.
"It's hard to see how you even get noticed in such a big, broad field without being shrill, sensational or a celebrity, and I'm none of those things and I'm never going to be any of those things," Patrick said in a September interview with Axelrod.
Summers reported from Charleston, South Carolina, and Pace reported from Washington.
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