Mayor Bill de Blasio, who has held off from endorsing Hillary Rodham Clinton for president, appeared to warm to his former boss in remarks Wednesday commending her "increasingly compelling vision" on immigration reform and other issues.

In April, when Clinton made official her second bid for the White House, de Blasio told NBC's "Meet the Press" that he wants "to see a vision" and "to see the substance" before granting an endorsement. De Blasio did not attend Clinton's June rally and speech on economic equality on New York City's Roosevelt Island.

But Wednesday, the Democratic mayor told WNYC host Brian Lehrer that Clinton's proposal for comprehensive immigration reform has been among the "kinds of things I think people in this country have been waiting to hear from a presidential candidate."

De Blasio still do not offer his nod to Clinton, a former secretary of state and the leading Democratic presidential hopeful. De Blasio was the campaign manager for Clinton's successful 2000 run for U.S. Senate. He also served during the presidency of her husband, Bill Clinton, in the U.S. Department of Housing and Urban Development.

De Blasio contrasted Hillary Clinton's campaign to that of another New York presidential candidate, Donald Trump.

"Look at juxtaposition with Trump, who is literally trying to undermine fundamental constitutional rights on things like birthright citizenship," de Blasio said. Automatic citizenship for children born in the United States is "part of our Constitution that I think has been a matter of consensus for generations and for good reason," he said.

The mayor said the billionaire real estate mogul, who currently leads polls of the crowded Republican field, should be taken seriously.

"I don't think anyone should take Donald Trump lightly," de Blasio said. "I say this particularly as a progressive, when you take conservatives lightly, you end up getting burned a lot of the time."

De Blasio predicted that Trump's past comments deriding Mexicans and the Vietnam War heroism of Sen. John McCain (R-Ariz.) as well as controversial past remarks about women would come back to haunt him.

Trump and Clinton's campaigns didn't immediately respond to requests for comment.