We not only would do no less, we did more. We supplied arms and food to our own armies, and those of most of our allies, including the Soviets. Of course it was a little easier for us, safe, more or less, behind the two largest oceans of the world, but it was also less urgent for the same reason.
We were truly the Arsenal of Democracy (and other forms of government). I remember reading that we spent something like 40% of GNP on defense in 1944, the peak year. I also read that the Soviets spent something over 60% of their GNP on arms during WW2, but who knows what to believe about Soviet economics - I don't even think that they really knew.
I certainly believe that we would make a gargantuan effort if directly attacked in a big way on our own soil. I could see a draft, and armies in the millions being sent to the Mideast to first destroy all hostile forces and then occupy their countries for a long time - decades. I just hope that the Chinese stay within their own borders while we're busy elsewhere.
The lesson that the Japanese learned about not waking a sleeping giant and filling him with a terrible resolve may have to be retaught to our enemies.