A congressional committee’s decision to subpoena a top Clinton aide who has been at the center of multiple controversies involving the former president and first lady has reinvigorated questions about Hillary Clinton’s ties to divisive political operatives and foreign entities.

Sidney Blumenthal’s informal Libyan intelligence memos to then-Secretary Clinton sparked controversy Monday after the New York Times revealed Blumenthal had advised Clinton using information he gathered through his involvement with a group of businessmen looking to capitalize on the fragile economic situation in Libya.