New York City Mayor Bill de BlasioBill de BlasioBiden only Democrat with strong positive favorability numbers: poll CNN forces DeBlasio to watch late-night comics ridicule him South Bend newspaper highlights Buttigieg's absences in recent months MORE (D) said Wednesday he is not ready to endorse Hillary ClintonHillary Diane Rodham ClintonNevada Senate passes bill that would give Electoral College votes to winner of national popular vote 2020 Dems break political taboos by endorsing litmus tests Iowa Democrats brace for caucus turnout surge MORE for president, but he's optimistic about her campaign.

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“What I’ve said very clearly is, I think the world of Hillary. I’ve worked with and for her for years,” he said during an interview on MSNBC’s “Morning Joe.” “The bottom line here is that we are at a moment in history where we need to hear a clear vision for investing in the economic reality.”

But de Blasio, who ran Clinton's 2000 Senate campaign, said he believes she is beginning to build a “progressive agenda” and that he is “optimistic” about her campaign.

“I’ve seen some clear signals, some clear ideas come out of her conversations in Iowa, certainly the speech on criminal-justice reform the other day I thought was very powerful, what she said yesterday on immigration. I think she’s beginning to fashion a progressive agenda,” he said. “I think a lot of us, understandably, want to hear the core ideas around the fight against inequality."

His comments come after Clinton staked out liberal positions on both criminal justice and immigration — and gave fresh indications that inequality will be a central topic in her campaign.