There used to be something called "treason"...but apparently the definition has been changed such that there is no point in which it is reached. Otherwise we'd have quite a few people guilty of it in the media, schools and government.
Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort. No Person shall be convicted of Treason unless on the Testimony of two Witnesses to the same overt Act, or on Confession in open Court. The Congress shall have Power to declare the Punishment of Treason, but no Attainder of Treason shall work Corruption of Blood, or Forfeiture except during the Life of the Person attainted.
I think his calls would be, at most, sedition.