The Logan Act makes it a felony and provides for a prison sentence of up to three years for any American, "without authority of the United States," to communicate with a foreign government in an effort to influence that government's behavior on any "disputes or controversies with the United States." Some background on this statute helps to understand why Ms. Pelosi may be in serious trouble.
President John Adams requested the statute after a Pennsylvania pacifist named George Logan traveled to France in 1798 to assure the French government that the American people favored peace in the undeclared "Quasi War" being fought on the high seas between the two countries. In proposing the law, Rep. Roger Griswold of Connecticut explained that the object was, as recorded in the Annals of Congress, "to punish a crime which goes to the destruction of the executive power of the government. He meant that description of crime which arises from an interference of individual citizens in the negotiations of our executive with foreign governments."
The debate on this bill ran nearly 150 pages in the Annals. On Jan. 16, 1799, Rep. Isaac Parker of Massachusetts explained, "the people of the United States have given to the executive department the power to negotiate with foreign governments, and to carry on all foreign relations, and that it is therefore an usurpation of that power for an individual to undertake to correspond with any foreign power on any dispute between the two governments, or for any state government, or any other department of the general government, to do it."
Griswold and Parker were Federalists who believed in strong executive power. But consider this statement by Albert Gallatin, the future Secretary of the Treasury under President Thomas Jefferson, who was wary of centralized government: "it would be extremely improper for a member of this House to enter into any correspondence with the French Republic . . . As we are not at war with France, an offence of this kind would not be high treason, yet it would be as criminal an act, as if we were at war." Indeed, the offense is greater when the usurpation of the president's constitutional authority is done by a member of the legislature--all the more so by a Speaker of the House--because it violates not just statutory law but constitutes a usurpation of the powers of a separate branch and a breach of the oath of office Ms. Pelosi took to support the Constitution.
There is also the old "aiding and abetting the enemy" during a time of war...