New York City Mayor Bill de Blasio has not yet endorsed Hillary Clinton for president, and it has left fellow Democrats scratching their heads.

De Blasio officially said on Sunday that he will not endorse Clinton until she has an "actual vision" for her campaign and candidacy, The Wall Street Journal reported.

Both Hillary Clinton and her husband have a long work history with de Blasio. Not only did the mayor work on Bill Clinton's presidential administration, but he also was the head of Hillary Clinton's team when she won the New York senate seat in 2000.

Both Clintons endorsed de Blasio when he successfully won the 2013 mayor race.

Furthermore, Hillary Clinton was one of the mayor's top fundraisers during that election and, upon de Blasio's victory, former president Bill Clinton swore him in at the inauguration.

Former U.S. Rep. Anthony Weiner told The Wall Street Journal that the Clintons should be "family" to de Blasio because of how much they have helped his career.

"...You don't ask a family member to lay out her résumé before you decide to support her," Weiner said. "This notion that he (de Blasio) is somehow this spokesperson for some wing of the party that Hillary needs to audition for, I think, is wrong and not helpful."

He added: "She [was] working on a progressive vision of health care when Bill de Blasio was still smoking pot at NYU or wherever he went."

Mark Green, a former public advocate, according to The Wall Street Journal, who is familiar with de Blasio, chimed in as well.

"While he's usually a very smart politician plotting his route to a goal, here there was a collision of goals: To be a national, if not international, voice against economic inequality, yet show his fidelity to a home-state friend and mentor," Green said. "He chose self-aggrandizement [over] Clinton loyalty."