He has said the same thing for a year now and even during his campaign about the Chinese currency. He is doing it more to appease some members of his political base.
What you need to look at are the administrations actions, not their words. The Treasury last year declined to label China as a currency manipulator. Now I don't think he wants to risk a trade war with China so he decides on a more moderate path of slapping tariffs on Chinese tire imports among other things.
I don't believe the president and his advisers are that dumb. They know if they get a real trade war with China, unemployment will rise further. The Obama administrations actions indicate he is not willing to go that far.