If there's noone to be afraid of, there's no justification for the incredible $400+ billion military budgets which provide enormous wins for defence contractors and their subsidiary industries (who all have the best lobbyists money can buy, which enables them to pressurise congressmen to quash or beneficially modify any legislation which has the potential to reduce profits or increase accountability). That's the nutshell. Anyone who tells you it's actually about preventing terror is deluded, lying or just gullible (i.e. someone who watches FOX). Before the War On Terror it was the War On Drugs. Before that the War On Commies and before that was the second World War. WW2, though it was fought for the right reasons, proved so lucrative for some businesses that they didn't want the government contracts and subsidies to stop. Ever. They didn't. Since the end of WW2 there has always been something for the Whitehouse to scare America with and basically every president since then has done exactly that. The threat of the USSR was vastly inflated, as were the threats of its supposed cronies Cuba, Laos, North Vietnam et al. The threat of Iraq was grossly inflated in 1991 (conveniently as the Cold War wound down) and again in 2002. Now we see Iran as the next "evil empire" poster-boy. If that "threat" fails to materialise (i.e. no justification can be made or made-up to invade/bomb the place) I wonder who would be next? Not China or North Korea - too able to defend themselves and not rich enough in resources. Venezuela, Bolivia, Argentina? Possibly - noone annoys Washington DC more than a country doing its own thing, taking control of its own resources and telling the US and its multinationals, the IMF and the World Bank to shove it.
The point is, whoever's at 1600 Pennsylvania Ave will always be beholden to the wishes of US multinationals, oil companies & defence contractors to name just three areas of pressure (the rest of the world often underestimates the power US lobby groups have on government). Black guy, white lady, yet another old white guy, won't matter that much who's president (a largely ceremonial title). The average American will get sold the same fear-mongering crap and told to shut up and do what he's told and buy some more consumer goods.