PresidentsDutyToFaithfullyExecuteLaws <– PDF version
President Barack “I lied, period” Obama recently issued an Executive Order that exempted many illegal aliens from deportation if they met certain nebulous requirements. It is alleged by His Most High Incompetence that this order would affect only about 5 million people, but there is no reason to believe that figure in favor of any higher number. Many have claimed that Obama’s particular Executive Order is illegal, since, by waiving a part of immigration law, he is failing to faithfully execute the laws per his oath of office as required by Article II, Section 1 of the Constitution. So far, 25 states have joined in a lawsuit seeking to have the order overruled, and the next Congress has claimed it will do the same (probably by endorsing and expanding it).
But the real question is: where does a President and his Justice Department toadies get the arrogance to ignore their oaths of office? That has already been answered by St. George Tucker, an early expositor of the Constitution  in a series of essays published in 1803:
Lastly; it is the duty of the president to take care that the laws be faithfully executed; and, in the words of his oath, “to preserve, protect, and defend the constitution of the United States.”
The obligation of oaths upon the consciences of ambitious men has always been very slight, as the general history of mankind but too clearly evinces. Among the Romans, indeed, they were held in great sanctity during the purer ages of the republic, but began to be disregarded as the nation approached to a state of debasement, that fitted them for slavery. Among Christian princes, they seem only to have been calculated for the worst, instead of the best purposes: monarchs having long exercised, and seeming to claim, not less than the successors of St. Peter, a kind of dispensing power on this subject, in all cases affecting themselves. A due sense of religion must not only be wanting in such cases, but the moral character of the man must be wholly debased, and corrupted. Whilst these remain unsullied, in the United States, oaths may operate in support of the constitution they have adopted, but no longer. After that period an oath of office will serve merely to designate its duties, and not to secure the faithful performance of them; or, to restrain those who are disposed to violate them.
Why does this kind of arrogance prevail? Because the officers of the government have adopted corruption and immorality as their mode of operation: what matters to them is the political expediency of the moment without regard for what is right, wrong, or important in the long term. It is not actually a legal matter: no court ruling will affect the basic corruption. Left unchecked, this level of corruption will eventually cause the republic to degenerate into tyranny. Montesquieu  notes:
When once a republic is corrupted, there is no possibility of remedying any of the growing evils, but by removing the corruption and restoring its lost principles; every other correction is either useless or a new evil.
We can only hope that the American people will be more discerning at the next presidential election.
 St. George Tucker, A View of the Constitution of the United States, Indianapolis, IN: Liberty Fund, p. 282, (1999). The original was published in 1803.
 Charles de Secondat, (Baron de Montesquieu), The Spirit of Laws, Book VIII, chapter 12.