Would why the Logan Act be struck down?
2. The U.S. government itself is often involved with multiple parties in foreign dealings, so "U.S. interests" are not always clearly defined.
3. In many cases it's almost impossible to define "any disputes or controversies with the United States" (the language of the law) in a way that passes muster in a criminal proceeding.
In the Flynn case, for example, he's accused of asking the Russians to veto a UN resolution on Israeli settlements in East Jerusalem because the Obama administration would not veto it. This should have disqualified Flynn from any consideration even to work as a janitor in the White House, but how would it be illegal? What exactly was the dispute or controversy of a foreign nation with the United States here?