These are career prosecutors ... not US Attorneys who the POTUS can fire, as did Clinton and eventually Bush.
The government is FULL of leftists in every branch, agency and department, who lay in wait for an opportunity like this to take down a Republican.
Judge Emmet Sullivan himself is, I believe, a Democrat .. perhaps the last honest one in DC.
Sullivan's political affiliation is not clear. He was first appointed to the bench by Reagan. He was subsequently elevated by both HW Bush and then by Clinton.
My guess is he's more interested in the law than in political ideology. Which, probably makes him sadly uncommon in today's judiciary.