TPC estimates that in 2013, Obama would collect revenues of 18.2 percent of GDP. McCain would bring in about 17.8 percent. Spending that year would be about 19.5 percent, according to the Congressional Budget Office, assuming the Iraq war will be winding down.
That's a difference of 0.4 percentage points in GDP. And it's important to measure spending and not revenues, because any deficit spending will result in inflation, which acts as a only vaguely-recognized tax on American citizens, but also anyone else who owns dollar bills.
*Sorry, third parties, but America's voting system is stacked impossibly against you. If another party enters the scene, it won't be as a third party, but as a future member of the two-party system, like it always has been.