It could be considered an act of disloyalty, which is not a crime, but it's not treasonous.
Treason, the only crime defined in the Constitution, consists of levying war against the United States or "adhering to" to an enemy, giving "aid and comfort." The Constitution does not specify a penalty, but a federal law does — anything from five years in prison to death.
U.S. & World
"Enemy" means a country or an entity that has declared war or is in a state of open war against the U.S. "Aid and comfort" must be something material, not words of encouragement. But the op-ed article fails both those tests, as it gives nothing material, and it is not in aid of an enemy.