Until recently Rod Rosenstein was the longest serving of the more than 90 US attorneys in America. But unless you lived in the state of Maryland, you probably would not have realised.

He never sought the limelight and quietly pursued criminal cases under both Republican and Democrat administrations. According to colleagues in Maryland he was a "by the book" and "apolitical prosecutor's prosecutor".

Suddenly, after being confirmed as the US deputy attorney general two weeks ago Mr Rosenstein, 52, finds himself at the eye of the storm.

After lambasting FBI director James Comey in a three page memo, the question everyone wants to ask Mr Rosenstein is whether anyone at the White House asked him to do it.

When a journalist reached him by phone Mr Rosenstein said: "I’m not going to talk about that (his memo). Are you surprised by that?”

Sean Spicer, the White House press secretary, said it was Mr Rosenstein who initiated the memo.

He said: “It was all him. That was a Department of Justice decision.”

But reports on Wednesday said it became clear that the memo - which says the decision to remove an FBI director "should not be taken lightly" - had become the justification for the move, the deputy attorney general threatened to quit.