Any move by special counsel Robert Mueller to go beyond collusion and obstruction of justice to probe possible money laundering by President Trump and his family could trigger a major constitutional clash — and present Congress with a massive political headache.

With nearly eight months gone by and some $7 million spent on Mr. Mueller’s Russia probe, speculation is mounting over when, whether and how the former FBI director might attempt to charge President Trump with a crime.

While sources say Mr. Mueller is “obsessed” with examining Mr. Trump’s network of business interests for potential money laundering infractions, there is a raging debate among legal scholars over whether that actually falls within the special counsel’s mandate.

That debate spilled into the open last week, when lawyers for Paul Manafort filed a lawsuit in U.S. federal court directly challenging Mr. Mueller’s legal authority to investigate and indict the former Trump campaign manager on pre-2016 money laundering charges.

The Manafort case could take months if not much longer to wind its way through the courts, and with that as a backdrop, several legal scholars told The Washington Times that any move by Mr. Mueller to pursue the money laundering and Mr. Trump’s personal finances would be on far shakier ground, and end up in the lap of Congress to adjudicate.

“The most important thing we do as a democracy is get together every four years to elect a president,” said Federalist Society co-founder Steven Calabresi, a law professor at Northwestern University. “And before the nation decides to overturn one of those elections, Congress will consider everything as it debates what sort of conduct is so harmful that it would justify doing that.”

Passing on to Congress criminal charges such as money laundering — and possibly triggering impeachment proceedings — would be driven by Mr. Mueller’s desire to sidestep the debate over whether a special counsel even has the authority to bring charges directly against a sitting president, the nation’s chief law enforcement officer, sources say.

Mr. Calabresi, who once clerked for conservative Supreme Court Justice Antonin Scalia, said Congress is exactly where charges against a sitting president should be debated.