Ford stopped being an American car company about when Mulally decided to eviscerate every single American car platform from the lineup, replace them with Eurotrash, and then put the abomination of Eco-Boost on every engine (including the Mustang).
General Motors is less so, but can still be considered American for what has been left alone. However, that isn't much given the amount of captive imports(Cruze, Sonic) and entirely converted divisions(e.g. the Opel^W Buick division).
About the only car company left that has mainly stayed American in the face of international pressure is Chrysler. Fiat has wisely kept them American without falling to environmentalist pressure to go Eurotrash.
If you're wondering, I've driven/owned mostly from those three. Not interested in something that sounds and operates like an oversized lawn mower.