Bill de Blasio's appeal to Elizabeth Warren falls flat

After expressing his respect for the Massachusetts senator and crediting her progressive leadership, de Blasio made his pitch: "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!"

The tone of de Blasio's post, and the suggestion that Sanders would have done the same for her, rankled many Democrats, who called it ham-handed and, in some cases, offensive. Sanders campaign leadership has been careful to avoid the appearance of pressuring Warren. Outside progressives, including those who have made the Warren-to-Sanders shift themselves, have also steered clear of making any public demands.

Nelini Stamp, of the Working Families Party, described de Blasio's approach as being "not the most helpful" tactic for coalescing progressive voters.

"I think the best way to bring Warren supporters on board is (to focus) on shared goals," Stamp said. "We can invite support without demanding it."

The Sanders campaign, which declined to comment on de Blasio's tweet, has been more cautious in its messaging since Warren, whose team also decline to comment, dropped out on Thursday.

"We've kept the relationship open and cordial from a staff all the way up to the principal level," Sanders campaign manager Faiz Shakir told CNN last week. "We respect her role in this process and believe that her vision for the country best aligns with Sen. Sanders, but the decision is up to her."

The tweet fell flat with outside Democrats, too, including journalist Connie Schultz, who is married to Ohio Sen. Sherrod Brown.

"When we deeply respect a person, Bill, we trust her judgment," Schultz tweeted in reply to de Blasio.

Others questioned the timing and de Blasio's claim that Sanders, if the roles were reversed, would have backed Warren by now.

"I thought it was very cringe-worthy on many levels. Elizabeth Warren doesn't need Bill de Blasio's advice on what's good for the progressive movement," said Brian Fallon, executive director of the liberal court reform group Demand Justice and Hillary Clinton's campaign press secretary in 2016. "I don't even think it's true, what he tried to say at the end of the tweet, that if the situation were reversed Bernie would have endorsed her already. I don't think that's true at all."

Sanders in 2016 waited until July -- a little less than a month after the final primary contest -- to endorse Clinton. The two did not share an ideological rapport in the way that Sanders and Warren do, but some Democrats remain miffed over the length of the process. Sanders would go on to campaign heartily for Clinton in the months ahead of the general election.

A de Blasio spokeperson did not immediately respond to a request for comment on the mayor's post.

Sanders did a receive a congressional endorsement on Tuesday, but not from Warren.

California Rep. Mark Takano, chair of the House Committee on Veterans' Affairs and co-chair of the LGBT Equality Caucus, backed the Vermont senator, touting in a video Sanders' longtime support for marriage equality and willingness to compromise on legislation benefiting veterans.

Earlier in the day, de Blasio on MSNBC's "Morning Joe" made the case that former Vice President Joe Biden, who now leads in the race for a majority of primary delegates, would be a risky choice for Democrats in November.

Biden, who first entered the Senate in 1973, has a record -- on issues like social security and his Iraq War vote -- that requires sharper scrutiny, de Blasio argued.

"Joe Biden hasn't been vetted. He was in a perfect position -- early front-runner and then everyone thought he wasn't going to make it, turned their attention to (former New York Mayor Mike) Bloomberg, Bernie, even to Warren for a while," de Blasio said. "Joe Biden has a lot of issues he needs to speak to. If we don't deal with it now, in the family, and have that blunt discussion, Donald Trump will."