A government that does not have the legal means and/or the political will to prosecute someone like Jane Fonda for open acts of treason had no business engaging in that military campaign in the first place.
There's little question that the U.S. could legally have prosecuted Jane Fonda for treason -- see Dr. Hank Holzer's "Aid and Comfort" for a detailed layout of that legal case.
And America had the political will to engage in the military campaign when it began, and also for years thereafter, until it was eventually eroded by leftist opposition and the lack of tangible success.
If you're going to argue that the U.S. shouldn't engage in any military action that the people might later disapprove, that pretty well eliminates everything...