Everything except the math perhaps. It's one thing to release big words during a campaign, it's quite another to translate them into reality.
At $50 a barrel, it's probably impossible to be profitable for oil companies. There's the tax break, however, as well as deregulation policies. The nitty-gritty of which is yet to be determined. Hopefully, it would end up fair to everybody lest "drill baby, drill" only benefits the drillers while the oil companies are overflowing with supply.
Well, if the domestic supply is cheap, dependency on Canadian and Mexican or even Venezuelan imports might significantly decrease. The rest of the supply could boost the country's oil export. Add to it the factor that foreseen stricter implementation of sanctions against Iran and Venezuela might deprive the world market of a million barrels a day.