No one knows how special counsel Robert S. Mueller III’s sprawling investigation into Russian political interference and potential White House obstruction will end, but Mueller is already changing how the nation’s capital does business.

His prosecutors have taken the rare step of pursuing some of President Trump’s former senior aides for failing to register as lobbyists for foreign governments, rattling the rarefied world of highly-paid professionals who advocate in Washington for traditional foreign allies, unsavory strongmen and other overseas clients.