In the situation alluded to, the one way congress has enforcement ability, is through the power of impeachment.

That is how they ensure that the President follows the constitution and enforces the laws that congress passes.

The people have enforcement power through the vote, the congress through impeachment.

Remember that the impeachment powers also extend over the judiciary, where the people usually don't have the power of the vote.

It can not be over stated the importance of the power of impeachment.

Not to get sidetracked from the original topic of regulation too much, I just wanted to point out the importance of enforcement to successful regulation, and the parallel of constitutional enforcement to successful government. If you don't maintain enforcement all the way to the top, be it Ken Lay or George Bush, then all the regulations (or constitutional provisions) in the world won't help you.