To understand the magnitude of Obama's action, we must again consider the above-cited fact that both chambers of Congress passed DOMA by overwhelming majorities reflecting the will of the people that marriage be defined, for legal and policy purposes, as it always had been. Also, no federal appellate court has ruled the statute unconstitutional.
As he has in so many other areas (EPA, the offshore drilling ban, IMF), Obama has usurped the authority of the other two coequal branches of government to make himself, in effect, not just chief executive but super-legislator and a supreme judicial authority.
Holder admitted in his statement that the Justice Department "has a longstanding practice of defending the constitutionality of duly-enacted statutes if reasonable arguments can be made in their defense," but not otherwise.
But it is preposterous to suggest there are no reasonable arguments to defend the statute when 5,000 years of human history and the express act of Congress fly in the face of that statement. According to professor John Yoo, "in the few cases that the Supreme Court has heard gay rights cases, it has never adopted (the standard Obama is applying)."
In announcing a new standard, Obama claims that the legal landscape has changed in the 15 years since DOMA was passed. You know the drill: Society has "evolved." That's highly dubious in view of the fact that even people in some liberal states have expressed their preference for preserving the traditional definition of marriage. Further, it is not Obama's place to make this determination, especially when the people have already done so in such emphatic terms through their duly elected congressmen. If the people want the law changed, they can lobby their congressmen to change it or marshal their lawyers to argue their position in actual cases before the courts.
In response to leftists arguing that President George W. Bush also declined to enforce a federal statute, Yoo says that Obama's action is distinguishable. Bush did so in cases in which he was resisting congressional intrusions into the executive's constitutional authorities in the area of national security. Here there are no alleged encroachments on executive authority; it's just that Obama has a different opinion than the American people and has decided to implement it unilaterally.
So now we have an imperial president who is refusing to enforce a law passed by powerful congressional majorities while persisting in enforcing a law (Obamacare) that two federal courts have already invalidated. The only common denominator is that Obama believes he is the law.