That whenever any Form of Government becomes destructive of these ends...

The Constitution of The United States is the Supreme Law of the Land. The President must make an oath agreeing to uphold the Constitution. According to Article Two, Section One, Clause Eight:

Before he enters on the Execution of his Office, he shall take the following Oath or Affirmation:— “I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States.”

According to that same Constitution, and supported by an excellent School House Rock presentation, 

Congress passes a bill, the President signs it and the bill becomes a law. No individual Congressman, Senator, or President has the power to make law, change a law, or void a law. failure to enforce a law puts the President in violation of his oath and the Constitution.

The Constitution is deliberately designed with a balance of power. The Congress makes law, The Courts interpret the law, the Executive branch carries it out. You should have learned this is 9th grade civics. The President is not a king, he cannot dictate law, or change a law.  He is a chief executive, no more. The founders just fought a war to get rid of a king, and wanted no part of another.

As pointed out by Mr. B, when the President fails to obey a law, why should the average Joe? Look, ObamaCare is a disaster. Without arguing the merits of the idea, the law itself is poorly written and conceived. But it is not up to the President to determine what parts of the law he likes and doesn't. Failure to enforce the law as written is grounds for impeachment.

The President may have slammed back a tumbler of bathtub gin during Prohibition, but he still sent Elliott Ness out to enforce the law. It can be no other way. Enforce the Law until it is changed legally by Congress. There is no second option. No matter how much ObamaCare it hurts you, me or my neighbor it is the law. We cannot live in a free society when the President functions like a King.