New York City Mayor Bill de Blasio Bill de BlasioNew York again pushes back in-person classes The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump contradicts CDC director on vaccine, masks De Blasio to furlough himself, 494 other staff members amid financial crunch: report MORE (D) urged Sen. Elizabeth Warren Elizabeth WarrenWarren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon No new taxes for the ultra rich — fix bad tax policy instead MORE (D-Mass.) to endorse Sen. Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE’s (I-Vt.) presidential campaign Tuesday, claiming Sanders would have done the same if the situation were reversed.

Warren said she would not immediately be endorsing a candidate when she ended her campaign last week.

“I deeply respect @ewarren. Our nation + our party is better + more progressive because of her leadership. Now our progressive movement needs her more than ever,” de Blasio tweeted Tuesday. “Senator, if the shoe were on the other foot @BernieSanders would have already endorsed you. We have.”

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I deeply respect @ewarren. Our nation + our party are better + more progressive because of her leadership. Now our progressive movement needs her more than ever. Senator, if the shoe was on the other foot @BernieSanders would have endorsed you already. Please join us! — Bill de Blasio (@BilldeBlasio) March 10, 2020

De Blasio, who ended his own presidential campaign in September, endorsed Sanders last month.

Several other former White House hopefuls have backed former Vice President Joe Biden Joe BidenCast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response Biden tells CNN town hall that he has benefited from white privilege MORE in what has become a two-person race, including former Rep. Beto O’Rourke (D-Texas), former South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBogeymen of the far left deserve a place in any Biden administration Overnight Defense: Woodward book causes new firestorm | Book says Trump lashed out at generals, told Woodward about secret weapons system | US withdrawing thousands of troops from Iraq A socially and environmentally just way to fight climate change MORE, and Sens. Kamala Harris Kamala HarrisScott Walker helping to prep Pence for debate against Harris: report California family frustrated that governor, Harris used fire-damaged property for 'photo opportunity' Moderna releases coronavirus vaccine trial plan as enrollment pushes toward 30,000 MORE (D-Calif.), Cory Booker Cory Anthony BookerDHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility Black Voters Matter Fund deploying voter outreach caravans in 12 states to drive turnout MORE (D-N.J.) and Amy Klobuchar Amy KlobucharEPA delivers win for ethanol industry angered by waivers to refiners It's time for newspapers to stop endorsing presidential candidates Biden marks anniversary of the Violence Against Women Act, knocks Trump and McConnell MORE (D-Minn.).

Biden has a lead in pledged delegates after a strong finish in South Carolina and last week's 15 Super Tuesday races.

Six more states are holding primary races Tuesday, including the 2020 general election battleground state of Michigan.