US is not particularly protectionist (compared to world average). The problem is double standards. For example:

• FDA or DoA regulates what is considered food in US and what is not. So, Scottish haggis (sp?) is not considered suitable for human consumption, as are not some kinds of Italian mortadella, German saugages, some cheeses etc. Nobody blames US for that. However, when EU standards put lower limits on hormones and antibiotics in meat (based on well documented studies showing them harmfull, especially for children), US cries 'protectionism!' and uses tame WTO 'arbitrators' to push their meat down European's throat. Now they are trying the same with genetically modified food; more precisely, they are trying to forbid labeling GM food in Europe, calling it protectionism. (I personally think that furor over GM food is blown out of proportion, but that's besides the point.)
• US and EU are constantly bickering over subsidies (mostly indirect) for commercial aircraft manufacturers (Airbus and Boeing). Several years ago an agreement was signed about that, and US side is unable to show that EU is in breach of it. When European countries buy military aircraft, it is normal that US companies compete without discrimination (and so recently Poland has chosen F-16 over European choice of JAS39 Grippen, Rafale and Eurofighter). But, when USAF suddenly decides it needs 50 or so new tankers, EADS/Airbus is told they need not apply with A330 - that is reserved for Boeing's surplus 767s and, haeven forbid, it is not indirect subsidy. Similarly in competition for various elint and sigint aircraft (now likely to be consolidated in a single platform) - British need not apply with their Nimrod variants...
• Steel story is rehashed too many times to repeat it again...