“Fundamental to a President’s fidelity to [faithfully execute his oath of office] is the Constitution’s demand that the President … disentangle his private finances from those of domestic and foreign powers. Never before has a President acted with such disregard for this constitutional prescription.”

The suit could open a new front for Trump as he navigates investigations by special counsel Robert S. Mueller III and congressional committees of possible collusion between his associates and the Russian government during the 2016 presidential campaign.

If a federal judge allows the case to proceed, Racine and Frosh say, one of the first steps will be to demand through the discovery process copies of Trump’s personal tax returns to gauge the extent of his foreign business dealings. That fight would most likely end up before the Supreme Court, the two said, with Trump’s attorneys having to defend why the returns should remain private.