New York City Mayor Bill de Blasio conceded in a radio interview Friday that he had a tough time defending Hillary Clinton during the Democratic primary over her refusal to release the text of her paid speeches to Wall Street firms.

"It's a statement of fact. It was hard to defend," the mayor and Clinton surrogate said in an interview on the Brian Lehrer show. "It's understandable why the media and the people demand that certain information come forward."

"I understand these things are hard to talk about," he added, explaining that he found it hard to defend her on "the disclosure issue."

During the Democratic primary, as Clinton refused repeated challenges from her chief opponent, Sen. Bernie Sanders, I-Vt., to release her Wall Street transcripts, de Blasio said publicly that he wasn't bothered by her speeches.

"I don't care about those speeches. I care about what's in her platform. Her platform would reign in Wall Street excesses more even than Bernie Sanders would," the mayor said in March during an interview on MSNBC's "Morning Joe."

"She has the sharpest platform for addressing the Wall Street crisis that any candidate has had since the Wall Street crisis, and that's out loud, and that's what she'll be held to. That's what matters in this election," he said.

However, de Blasio revealed privately that he struggled to downplay her refusal to release the speeches, according to a series of emails published by the hacking group WikiLeaks.

In an email dated March 2, de Blasio wrote to Clinton's campaign chairman, John Podesta, in reference to his MSNBC appearance, "I'm trying, brother, but this one is hard to defend."

On Friday, de Blasio didn't deny writing the email, and he argued that what he said privately about Clinton's Wall Street speeches doesn't clash with what he said publicly.

"I think those two [statements] actually are consistent," the mayor said. "The fact that I said publicly that I believe it in my heart that her platform, what she has committed to in the cool light of day this is what she will do and she will be held accountable to the platform — that's what matters."

"And the platform is the most progressive of any Democratic nominee in many decades," de Blasio said. "That's what matters. And my absolute conviction that Hillary will take on powerful interests to do things like tax the wealthy and raise the minimum wage," he added.

Clinton's lucrative speaking career came under close scrutiny during the Democratic presidential primary when Sanders argued repeatedly that she was in the pocket of Wall Street lobbyists. She refused then and she refuses now to release the text of her Wall Street speeches.

A review of the Clintons' 2015 tax returns show they took in a combined $6.72 million from paid speeches. Their 2015 tax returns, which were released last week, also showed they paid an effective federal tax rate of 34.2 percent, and that they had an adjusted gross income of $10.6 million.

This is a notable decline from 2014, when Hillary Clinton alone took in $10.5 million in speaking fees, combining with Bill Clinton's $9.7 million on the way to an adjusted gross income of nearly $28 million. In 2013, Hillary Clinton earned $9.6 million from speaking to various groups.

The Democratic nominee stopped giving paid speeches after she announced her candidacy in April of last year.