With the U-boat vs destroyer incidents, you have them in vicinity of convoys, subs trying to do ID through periscope (and remember there were ex-US ships in RN service) so the "accident" excuse is plausible, whether or not it is truly the case. It's really really hard to make the case that firing on the Texas was an oops - even if it really was.
While the US military in early 1941 was very early in to expansion and modernization, industry had been ramping up to support the Allies since the war started, as happened in WWI. US in the war against Germany 6 months early actually makes it worse for Germany, as the USN comes in early to help the Brits, US war production begins total mobilization 6 months early and there is no Pacific distraction. With the USA on a war footing, will Japan still attack - hard to say. Certainly some of fleet will be in the Atlantic, but what is in the Pacific - air and naval and land - will be on much higher alert.