A COMPELLING CASE FOR A JUST MISSION…. If the point of President Obama’s speech last night on U.S. intervention in Libya was to answer the “Why Libya?” and “Why now?” questions, it was a great success. Indeed, as a relative skeptic of this mission, the remarks exceeded my expectations.

These two paragraphs, in particular, drove home what we’re doing and why.

“It is true that America cannot use our military wherever repression occurs. And given the costs and risks of intervention, we must always measure our interests against the need for action. But that cannot be an argument for never acting on behalf of what’s right. In this particular country — Libya; at this particular moment, we were faced with the prospect of violence on a horrific scale. We had a unique ability to stop that violence: an international mandate for action, a broad coalition prepared to join us, the support of Arab countries, and a plea for help from the Libyan people themselves. We also had the ability to stop Gaddafi’s forces in their tracks without putting American troops on the ground.

“To brush aside 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. Some nations may be able to turn a blind eye to atrocities in other countries. The United States of America is different. And as President, I refused to wait for the images of slaughter and mass graves before taking action.”

In terms of making the case for a humanitarian-based mission, this is pretty compelling. In fact, the president repeatedly emphasized what makes this mission just and morally necessary.

It became easy to imagine Obama, listening to his team a few weeks ago, and being told that he could prevent the massacres of thousands by assembling a coalition, with limited risks to United States, earning international imprimatur, and launching a short-term mission.

This isn’t about taking oil reserves or no-bid contracts for the administration’s buddies; this is about Obama’s desire to avoid images of mass graves, knowing he could have prevented it.

What’s more, I was also struck by the president taking a moment to boast about just how effective U.S. officials have been of late.

“[I]n just one month, the United States has worked with our international partners to mobilize a broad coalition, secure an international mandate to protect civilians, stop an advancing army, prevent a massacre, and establish a No Fly Zone with our allies and partners. To lend some perspective on how rapidly this military and diplomatic response came together, when people were being brutalized in Bosnia in the 1990s, it took the international community more than a year to intervene with air power to protect civilians. It took us 31 days.

“Moreover, we have accomplished these objectives consistent with the pledge that I made to the American people at the outset of our military operations. I said that America’s role would be limited; that we would not put ground troops into Libya; that we would focus our unique capabilities on the front end of the operation, and that we would transfer responsibility to our allies and partners. Tonight, we are fulfilling that pledge.”

Well, sure, when you put it that way, the administration’s work has been pretty impressive.

Like a lot of high-profile Obama speeches, this one seemed geared towards anticipating and answering questions. Why didn’t we go on the offensive sooner? Because we needed time to assemble a strong international coalition. Why isn’t regime change part of the mission? Because it would shatter the coalition and exceed the legitimacy of our mandate. Why not wait for sanctions and diplomatic pressure before using force? Because Gadhafi was poised to commit horrible atrocities, and create a refugee crisis for neighboring countries like Egypt, if the coalition hadn’t acted precisely when it did. Why isn’t the U.S. “taking the lead” in the larger mission? Because “real leadership creates the conditions and coalitions for others to step up as well; to work with allies and partners so that they bear their share of the burden and pay their share of the costs; and to see that the principles of justice and human dignity are upheld by all.”

And yet, as persuasive as I found all of this, and as earnest and strong as I perceived Obama to be last night, I still can’t say with any confidence what the end game of this mission is. I still don’t know what happens if rebels and Gadhafi forces fight to a standoff. I’m still not sure what kind of responsibilities the West will have to keep Libya together if the regime falls.

A transfer of responsibility will shift from the United States to NATO tomorrow, but no one can say with any certainty when U.S. forces can extricate themselves altogether, or even what kind of conditions would make that possible.

As a matter of conscience, the president’s case stood on a strong foundation. But that doesn’t negate lingering questions that may not have answers anytime soon.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.