NAFTA actually made it easier for automakers to move assembly plants to Mexico and Canada. In the end, if you're looking to "buy American", any car manufacturer owned by a US parent company will ultimately benefit from your purchase regardless of how many "foreign" parts are in the vehicle. Buying a Toyota just because it is made in the US is still benefiting a Japanese company in the end.
Where it gets complicated is US companys own major percentages of foreign companys and like wise the other way around. Buying anything that is manufactured in the US regardless of parent company will keep a US employee employeed, ultimately helping the US economy from the bottom up. Ofcourse, with taxes the way they are many companies will eventually out source everything. Bottom line is with this "global economy thing"......YOU CAN'T WIN!
