Deportation was not the word used by the Lincoln administration. Their order, as transmitted through Stanton, was to "send C. L. Vallandigham under secure guard to the headquarters of General Rosecrans to be put by him beyond our military lines and in case of his return within our lines he be arrested and kept in close custody for the term specified in his sentence."
Still don’t see how this is legal. The President can send American citizens to people with whom the US is at war?