Gene L. Dodaro is not a household name. He is a mild-mannered man who is rarely seen without a necktie and dark suit, and who speaks in a flat, matter-of-fact tone. He has worked for the federal government since 1973.

Yet, his retirement in December may well set off a separation-of-powers battle royale between President Donald Trump and Congress. Dodaro is the head of the Government Accountability Office, which has been a thorn in the president’s side during his second term.