"....Thus, unless you are planning to store gargantuan tanks of hydrogen....."
How else are you going to store the gargantuan amounts of hydrogen it would take to fuel the US if not in gargantuan tanks? I may be stupid, but I'm smarter than you!
If we were to store as much energy in Hydrogen fuel as we currently store petrol fuel I suspect we would still not make 1/10 of 1% difference in the molar fraction of oxygen in the atmosphere. The idea of keeping enough hydrogen stored to significantly affect the atmospheric concentration of oxygen is ludicrous to say the least.