Then films like Air Force One, Independence Day, and the bizarrely interchangeable Olympus Has Fallen / White House Down combo take it a step further, depicting the president as a gun-toting ass-kicker who's immune to the seductive charms of stupid "politics."
So What's The Deal?
Americans tend to see Congress as a bunch of old, out-of-touch white men deep in the pockets of special interests. We don't agree on much these days, but we do agree on how much we hate the people we elected to office. In real life, the American government is protected by a system of checks and balances that don't allow any one branch (or person) to completely take over. But an efficiently run bipartisan commission doesn't readily lend itself to shootouts with M16s or badass one-liners.