Problem-plagued U.S. presidents love to travel abroad, to be welcomed by overhead jets, sword dances and lots of pomp and photo-ops. But then they have to return. Now that President Donald Trump is back, he'll face the agony of a special counsel's investigation that could imperil his presidency. The probe by Robert Mueller into Russian interference in the 2016 election is deadly serious, and is likely to be wide-ranging and protracted. That's why the president and some of his associates are, in investigative parlance, "lawyering up."

The former director of the Federal Bureau of Investigation, Mueller is empowered to probe links between Russians and the Trump universe. This includes "any matters" that arise from the investigation. Mueller can be counted on to be discreet, fair and tough. He'll look at whether there was any coordination between Russian authorities and campaign personalities, any financial links or money laundering, and whether the president tried to obstruct the investigation.

Evidence so far is only circumstantial. Yet there's plenty of it, including a pattern of deceptions and lies about Russian connections that causes Republican concern.