Rosenstein is not the acting head of DOJ. Whitaker is. And Rosenstein was taken off being the supervisor of Mueller. At some point Trump is going to release the unredacted FISA documents, including the renewal signed by Rosenstein.
Agreed. However, there are currently no congressional committees that are asking for his testimony, much less sending him a subpoena. The House now won't, and the Senate hasn't. It would take some amount of time for that to happen, and Barr will likely be approved by then.
Rosenstein, on the other hand, had given Trump nothing. RR was instrumental in the judicial cover-up of the Uranium One deal. Trump was accustomed to hiring people, giving them a chance and then firing them if they didn’t work out. That cannot happen with much in the government. Whoever recommended RR knew the he was dirty. Was it Maryland Dem Congressman Elijah Cummings, a sly fox? Dems play hardball.