The deputy attorney general's testimony comes after Trump friend and Newsmax CEO Chris Ruddy said Monday that Trump was considering "terminating" the special counsel who is overseeing the Justice Department's wide-ranging inquiry into possible collusion between the Trump campaign and Russian officials.
Daniel Coats, the current director of national intelligence, head of the National Security Agency, Mike Rogers and retired NSA deputy director Richard Ledgett have agreed to be interviewed by the special investigators this week.
President Trump has "no intention" of firing the special counsel investigating Russia's interference in the 2016 presidential election, a senior spokeswoman for Trump told reporters traveling with the president Tuesday.
But Republican former House Speaker Newt Gingrich, who initially praised Mueller's selection, said he has changed his mind because the special counsel is hiring some "bad people".
"The FBI leak of information regarding the President is outrageous, inexcusable and illegal", said Mark Corallo, a spokesman for Trump's legal team. Brian Schatz about the scope of Sessions' recusal, Rosenstein said Sessions "actually does not know what we're investigating, and I'm not going to be talking about it publicly". But both appearances, however, are being overshadowed by Sessions' public appearance at a Senate intelligence committee hearing.
As Mueller builds his legal team, Trump's allies have begun raising questions about the former Federal Bureau of Investigation director's impartiality, suggesting he can not be trusted to lead the probe.
A spokesman for Mueller's team declined to comment on Wednesday.
Ruddy said in an interview Monday with Judy Woodruff of PBS, "I think he's weighing that option".
Trump was forced to fire Flynn in February after he misled the White House about his contacts with Russian officials previous year as a member of Trump's transition team.
The responsibility for appointing (or theoretically firing) Mueller lies with Rosenstein because his boss, Attorney General Jeff Sessions, recused himself in March from all investigations involving Russian Federation and the 2016 elections.
The original investigation was tasked with examining reported ties between Mr Trump's election campaign and Russian Federation but after Mr Comey's testimony the President's motives are now under the microscope.
Second, it suggests that not only is the special counsel's investigation reaching upward in the White House but that is also broadening out from simply an attempt to answer the question of the breadth of Russia's hacking and whether it caught up any Trump officials in it.
White House spokeswoman Sarah Huckabee Sanders said: "Chris speaks for himself".
At the time, Sessions said he was recusing himself only because he was involved in the 2016 campaign as an adviser to the Trump campaign.