The special counsel’s nearly two-year probe of Russian interference in the 2016 elections may have let the president himself mostly off the hook, but one sector emerged positively scathed: international lobbying.

Robert S. Mueller III’s investigation resulted in the convictions of onetime lobbyists, of course, but more consequentially, it put an unprecedented glare on the sometimes shadowy foreign influence campaigns that play out on U.S. soil — and the disclosure rules of those engagements.

In a sign of what may come next, the Justice Department recently put a former prosecutor from Mueller’s team, Brandon Van Grack, in charge of the unit that enforces the 1938 law known as the Foreign Agents Registration Act, which governs lobbying efforts on behalf of foreign governments and foreign political clients.

K Street is on notice, and lawyers and lobbyists say the FARA unit is already pursuing new cases that have not yet been made public. On Capitol Hill, Republicans and Democrats are considering a rewrite of the 81-year-old law, including giving the unit more authority to investigate possible violations.

“The increased focus on FARA is not a flash in the pan,” said Joshua Rosenstein, a partner at Sandler Reiff Lamb Rosenstein & Birkenstock who focuses on foreign lobbying law.