When clients tell Mercury Public Affairs, a consulting and lobbying shop with 18 offices worldwide, that they’re concerned about Donald Trump’s possible return to office, the firm has just the person to ease their nerves: Bryan Lanza. “He gives them assurances that there will be life after Nov. 5,” said one of the colleagues, referring to Election Day.Lanza declined to comment through a Mercury spokesman. A Trump spokesman did not respond to questions.Eight years after Trump entered politics promising to reduce the influence of Washington lobbyists — to “drain the swamp,” as he put it — advocates for corporate interests,...