Quoting the entire post from Greg Sargent:

Whatever you think of Obama's decision to authorize military action in Libya without the approval of Congress, it needs to be stated that in so doing, Obama ignored the lessons of history as he himself has defined them.

A number of people have pointed to Obama's quote from 2007 in which he told the Boston Globe that he doesn't believe the President should have the power "to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation." But in a sense this is the wrong part of Obama's 2007 quote to focus on, because as everyone knows, a president can easily get around this legal problem by labeling a foreign crisis a threat to American national security, as Obama has now done in the case of Libya.

Rather, the more important part of Obama's 2007 quote is this one:

In instances of self-defense, the President would be within his constitutional authority to act before advising Congress or seeking its consent. History has shown us time and again, however, that military action is most successful when it is authorized and supported by the Legislative branch. It is always preferable to have the informed consent of Congress prior to any military action.

Putting aside the legal questions here, Obama is acting in violation of the lessons he once took from history. Along these lines, Dem Rep. John Larson of Connecticut, who added his voice to the criticism of Obama's decision, made an important point today. Larson noted that even if Obama technically is in compliance with the War Powers Resolution, he is violating its spirit: "To insure that the collective judgment of both the Congress and the President will apply to the introduction of United States Armed Forces into hostilities."

Obama very well may have had his reasons for not consulting Congress as extensively as he might have -- time was of the essence; the president expects this to be wrapped up quickly; he doesn't envision this as a full-scale war; etc. But it's very obvious that Obama's approach is at odds with his own instincts and his own reading of history, at least as it stood when he was the reader and other presidents were the lead actors.

I'll just add there's nothing "self-defense" or "imminent threat to the nation" about this, whatever you think of it.