President Barack Obama stuck to the facts in his speech on Libya, but as others have pointed out, he has flip-flopped on the fundamental question of whether he needed congressional approval for military intervention.

Also, Obama sought in his address to minimize the military costs to the United States by saying NATO will now take the lead. But the fact is that the United States pays the largest share of NATO’s budget — one of a couple of key omissions by the president.

Obama, who addressed the nation in a prime-time speech March 28, gave his justification for quick military intervention. He noted that he consulted with congressional leaders. However, he did not get congressional approval.

Obama, March 28: Ten days ago, having tried to end the violence without using force, the international community offered Gadhafi a final chance to stop his campaign of killing, or face the consequences. Rather than stand down, his forces continued their advance, bearing down on the city of Benghazi, home to nearly 700,000 men, women and children who sought their freedom from fear. At this point, the United States and the world faced a choice. Gadhafi declared he would show “no mercy” to his own people. He compared them to rats, and threatened to go door to door to inflict punishment. In the past, we have seen him hang civilians in the streets, and kill over a thousand people in a single day. Now we saw regime forces on the outskirts of the city. We knew that if we wanted — if we waited one more day, Benghazi, a city nearly the size of Charlotte, could suffer a massacre that would have reverberated across the region and stained the conscience of the world. It was not in our national interest to let that happen. I refused to let that happen. And so nine days ago, after consulting the bipartisan leadership of Congress, I authorized military action to stop the killing and enforce U.N. Security Council Resolution 1973.

As our fact-checking colleagues at Politifact and the Washington Post have already noted, Obama has changed his position 180 degrees on the need for a president to get congressional approval to use force in a situation such as this.

During the 2008 presidential campaign, the Boston Globe asked Obama about the president’s constitutional authority to use military force without congressional approval in "a situation that does not involve stopping an imminent threat." Obama, a Harvard-trained lawyer who opposed the Iraq war, told the Globe in a candidate Q&A that was published Dec. 20, 2007, that the president has no such authority unless there is "an actual or imminent threat to the nation."

Question: In what circumstances, if any, would the president have constitutional authority to bomb Iran without seeking a use-of-force authorization from Congress? (Specifically, what about the strategic bombing of suspected nuclear sites — a situation that does not involve stopping an IMMINENT threat?) Obama: The President does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation. As Commander-in-Chief, the President does have a duty to protect and defend the United States. 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.

In his speech, the president did not say there was an imminent threat to the United States, but rather he spoke more broadly of our "national interest." He also spoke of "America’s responsibility as a leader and — more profoundly — our responsibilities to our fellow human beings under such circumstances would have been a betrayal of who we are."

Also, the president said in his speech that the cost of military actions in Libya "to American taxpayers will be reduced significantly" because NATO "has taken command of the enforcement of the arms embargo and the no-fly zone." NATO — the North Atlantic Treaty Organization — made that announcement March 27.

However, as the Associated Press points out, it’s not clear what difference that will make to U.S. taxpayers given NATO’s reliance on the United States for money and resources.

NATO is composed of 28 member countries, which make direct contributions based on a cost-sharing formula. The United States is responsible for about 22 percent of NATO’s civil, military and security programs — the largest of any member country.

According to the nonpartisan Congressional Research Service, the Obama administration requested $811.6 million for those three NATO programs in the fiscal year 2011 budget request. (Congress has yet to approve the budget, even though the fiscal year began Oct. 1, 2010.) Of that, $462.5 million would go to NATO’s military budget. However, that’s just in direct contributions. The Department of Defense said that through Monday, March 28, the United States had spent $550 million on the mission in Libya — exceeding the U.S. direct contributions to NATO’s annual military budget.

We do not know what the future costs will be to American taxpayers, but then again neither does the president.

Similarly, the president omitted some relevant context when discussing support for the mission among Arab countries. Obama was correct in saying that the "Arab League appealed to the world to save lives in Libya." The Arab League, which has 22 members, supported the mission to impose a no-fly zone at an emergency meeting in Cairo on March 12. Since then, however, the Washington Post has reported that Arab League Secretary-General Amr Moussa has expressed concerns about the "broad scope" of the military attacks.

Otherwise, the president stuck to the facts in justifying the need for U.S. intervention. For example, Obama accurately quoted Libyan leader Moammar Gadhafi’s threat to go "door to door" to find and kill fellow Libyans who oppose him.

Gadhafi, Feb. 22: I am the leader, Moammar Gadhafi, defender of millions. I call upon millions from the Sahara to the Sahara. And we will march in order to purify Libya inch by inch, house by house, home by home, village by village to purify the country.

In the end, we leave it for you to decide if the president acted preemptively and without constitutional authority — questions that have come up in other conflicts without resolution.