This is not protected speech. It is naked treason and was prosecuted as such during WWII.
Treason, perjury, libel, slander, and inciting a riot are not protected speech. Laws against sedition go in and out of fashion but treason is defined as a crime in our Constitution and it is providing aid and comfort to the enemy in wartime.
Just because we have free speech doesn’t mean you can say what you want. The way I see it, before someone opens his or her mouth to say something, it is best to engage the brain, What you say can have consequences. One needs only to remember that shouting fire in a crowded theater can get you in big trouble