I don't think it's about ideology as much as interests. In the 80s and 90s, the US was the world's most economically powerful country and was able to use free trade to further its own interests; the ideological arguments for free trade were constructed to justify policies which were deemed to be in the interest of the US and its owners. Now that the US is facing serious competition, protectionism is gradually becoming a more rational policy, and the public ideology of American politicians is adapting.