Deputy Attorney General Rod Rosenstein said he is satisfied with the work special counsel Robert Mueller has done so far as part of his investigation into Russian meddling in the 2016 election.

Rosenstein replied “yes” when, in an interview, he was asked if he was pleased with Mueller’s work.

“When we conduct criminal investigations, just as was true in Maryland, we don’t talk about the investigation while it’s ongoing,” Rosenstein, a former U.S. attorney for the District of Maryland, told NBC4. “So what the American people will see is only if and when a case is charged, and there are several cases that have been charged to date.”

The deputy attorney general tapped Mueller in May to oversee the investigation into Russia’s interference in the 2016 election after President Trump fired former FBI Director Jim Comey.

Since then, the president has repeatedly tried to discredit Mueller’s probe, calling it a “witch hunt,” and has criticized the Justice Department for failing to investigate Hillary Clinton, the Clinton Foundation, and the Uranium One deal.

Mueller and his team have so far charged four people as part of their probe: former Trump campaign chairman Paul Manafort and his business associate Rick Gates, former Trump campaign foreign policy adviser George Papadopoulos, and, most recently, former national security adviser Michael Flynn.

Flynn was the first person who worked for the Trump administration to face charges from Mueller’s investigation.

Both Flynn and Papadopoulos pleaded guilty for lying to the FBI about their respective contacts with Russia.