There's a restriction, it just has no teeth and no respect. The general welfare and commerce clauses are stretched far beyond their actual purpose in order to allow the US government to do pretty much whatever the hell they want, even if it completely invalidates the 9th and 10th amendments. The commerce clause was put in there so the federal government could strike down protectionist laws between the states.
Fact of the matter is the US government will do simply whatever people will allow it to get away with, which these days is quite a bit. It engages in ongoing, excessive coverups and blackouts of information in the name of 'national security' in order to prevent corrupt officials from being embarrassed or going to jail and if something DOES get leaked, the US will prosecute the leaker and a low-level patsy will be blamed and forced to resign just to be shifted to some comfy private industry position. Democrat or Republican, that's business in DC. People are killed just so a campaign donor can get a multi-million dollar defense contract. People are appointed to regulatory agencies from the very businesses they're supposed to be regulating.
The whole place is just about 100% irredeemable as anyone elected who actually does mean what they say is set aside into ineffectiveness because they won't play ball. Nothing's going to change unless something seriously bad happens to cause it as we're all still busy talking about how we need to vote for Obama because Romney is pretty much Satan or that we need to vote for Romney because Obama's gonna steal your house and give it to illegal immigrants. They're both empty suits who are bought and paid for by corporations and will continue the incestuous corporate-government revolving-door politics in DC.