The head of the Democratic Party criticized Republican leaders Tuesday for what he said was “such appalling silence” on the criminal charges brought against former Trump campaign aides by special counsel Robert Mueller.

Speaking at a Monitor-hosted breakfast for reporters, the Democratic National Committee chair, Tom Perez, said top GOP officials including Senate majority leader Mitch McConnell and House Speaker Paul Ryan kept silent in the face of “an assault not simply on the DNC but on our democracy.”

“It is clear the Russians were trying to traffic in the [Clinton campaign] emails and present them to … the Trump campaign so they could help Donald Trump get elected,” Mr. Perez charged. “You see with the indictment of Manafort and Gates that the rot went all way to the top of the campaign.”

Paul Manafort served as the Trump campaign’s chair and Rick Gates, a former business associate, as a campaign adviser. Both men were charged Monday with federal crimes by Mr. Mueller and pled not guilty in a court appearance. Another Trump campaign adviser, George Papadopoulus, pled guilty to lying to federal investigators.

The legal challenges surrounding the Trump campaign team notwithstanding, Perez was clear that if the Democratic Party wants to reclaim power in Washington or in individual states, it needs to rebuild.

Since his election as party chair in February 2017, Perez said, “we looked at what happened over the last eight years that resulted in the loss” of over 1,000 seats in state legislatures, 12 seats in the US Senate, and cut Democratic governorships from 28 to 15.

A key element of the rebuilding, he said, was changing the DNC’s mission. Rather than just focusing largely on helping elect a president every four years, Perez said, “we are the party that helps elect people, up and down the ticket, from the school board to the Oval Office.”

In addition to broadening the DNC’s mission, Perez also has the task of bringing together the very different ideological wings of the party represented by Hillary Clinton and Vermont Sen. Bernie Sanders.

“The issue of unity is something we have to fight for and continue to strive for every single day,” Perez said. “I am not oblivious to the fact that I walked into a DNC where we had work to do on the unity front.”

Unity is not universal in the Republican Party either, with former White House aide Steve Bannon threatening to lead primary challenges to sitting Republican senators.

“If Steve Bannon wants to continue to facilitate a circular firing squad on the Republican side, I am certainly not going to stand in the way of that,” Perez said.

While Perez was not leading the DNC during the 2016 campaign, he defended the fact that the DNC paid for opposition research conducted by the firm Fusion GPS, which hired a British spy to assemble the document. The White House has taken strong exception to the dossier.

“Opposition research is not simply something that ought to be done, it would be malpractice not to do it, especially when you have a presidential candidate who blew convention out of the window,” Perez said. “He didn’t disclose his tax returns, the first time that has happened in decades. He has a very shady relationship with Russian authorities.”