In January 2019, de Blasio and Secretary of Housing and Urban Development Ben Carson reached an agreement to change the operations of the New York City Housing Authority. The agreement created "specific requirements and milestones to address the serious health and safety hazards at NYCHA properties, including lead-based paint, mold, heat, vermin, among others".
In 2019, City Journal reported that during the de Blasio administration, "New York City’s budget has expanded by some $20 billion, and is expected to total about $93 billion for the coming fiscal year. Expenditures have ballooned three times as fast as the rate of inflation".
In April 2019, De Blasio announced his support for the Green New Deal and for legislation to ban the construction of glass and steel skyscrapers in New York City, citing environmental concerns and contribution to global warming. De Blasio also criticized the development at Hudson Yards in Manhattan.
On February 14, 2019, while addressing a rally in New York City about combating antisemitism, De Blasio said: "Maybe some people don’t realize it, but when they support the BDS movement, they are affronting the right of Israel to exist and that is unacceptable." De Blasio condemned Representative Ilhan Omar's remarks about Israel and pro-Israel lobbyists as "absolutely unacceptable" and "illogical".
In November 2019, de Blasio criticized former mayor Michael Bloomberg's apology for the stop and frisk policy, tweeting, "This is LONG overdue and the timing is transparent and cynical. With all due respect to my predecessor, we’ve spent six years undoing the damage he created with this bankrupt policy. We ended stop and frisk AND drove down crime. Actions speak louder than words." Police Benevolent Association President Patrick Lynch joined the Mayor in criticizing Bloomberg's apology as well.
On May 16, 2019, de Blasio announced that he would seek the Democratic nomination for president after releasing a YouTube video in which he said, "I’m Bill de Blasio, and I’m running for president because it’s time we put working people first." He was the first incumbent mayor of New York City to run for president since John Lindsay, who ran for the Democratic nomination in 1972.
During his campaign, de Blasio expressed support for increasing the federal minimum wage to $15 an hour. On June 19, 2019, he said, "We have to make sure there is a peace settlement in Afghanistan; it obviously has to involve the Taliban. Until that point, I don’t think it’s sensible to take out our troops." De Blasio advocated a robot tax and proposed to make large corporations responsible for five years of income tax from jobs that are automated away.
De Blasio's campaign failed to gain traction. He was unable to qualify for Democratic primary debates in September and October, which were seen as necessary events for his campaign to maintain viability. He regularly polled at 0% among Democratic primary voters, including in his home state. After failing to qualify for the third round of primary debates, de Blasio announced the suspension of his campaign on September 20, 2019. On February 14, 2020, de Blasio endorsed Sanders.