Clement Rollins is the special prosecutor appointed by the U.S. Attorney General in the matter of docket CRSP-00101, the investigation into the covering up of Josiah Bartlet's Multiple Sclerosis. He is described (hypothetically, ahead of his appointment) by Oliver Babish as "the most blood-spitting, Bartlet-hating Republican in the bar.", but in conversation with CJ as "a good guy". Ainsley Hayes says that he "takes his duties seriously, wants to get the truth, and he wants to avoid any appearance of impropriety or partisanship.".
In "Ways and Means" Rollins issues his first round of subpoenas, listing, presumably in most cases by their full legal names, the various members of the Bartlet family and White House staff who are at the top of his list. He was essentially 'taken out of the game' by CJ's tactic of encouraging the House of Representatives to step in, since she deliberately played up the White House's satisfaction and willing cooperation with the Rollins' investigation.