* Will Senate Dem leaders hold line on Social Security against “centrists”? Read of the morning: It’s good to see that Harry Reid and Chuck Schumer continue to hold the line against self-described centrists who insist that the best move for Dems politically is to agree to cuts in a popular program that has been a defining one for the Democratic Party for decades.

As that link details, there’s a growing rift among Dems over how to respond to the right’s demand for “entitlement cuts,” and the Dem approach to the issue will be a politically defining one this cycle.

* The administration’s view of their handling of Libya: Karen Tumulty has a very fair write up of our domestic political argument over Obama’s handling of Libya, including this succinct wrap-up of the administration’s view of all the criticism:

The White House has replied by asking, what were the president’s choices? To go in early, they say, would have meant to do it unilaterally. To refuse to act when Libyan leader Moammar Gaddafi was declaring war on his own people would have meant the possibilty of standing by as thousands were slaughtered.

The key here remains that we still don’t have a clear sense of what success would look like.

* How do we know when humanitarian intervention has succeeded? Eugene Robinson makes the key point that even if the goal is to protect civilians, how do we know when we’ve achieved that in a long-term sense? Is achieving it in a long term sense even the goal here, and if so, how do we get there?

Robinson on the shifting goal of protecting civilians: “The goal must be to prevent the bloodbath, not just reschedule it.”

* NATO takes charge: NATO is now assuming control of the no-fly zone, but the key question remains how, or whether, NATO will assume control of the core goal of protecting civilians.

* No Oval Office address on Libya? Obama is reportedly resisting pressure to deliver an Oval Office address clarifying our Libya mission, in part because he doesn’t want to give this short-term engagement the status of a real war.

* Paul Krugman keeps trying to redefine “serious”: As Krugman tirelessly continues pointing out, the evolving Washington consensus in favor of prioritizing the deficit now with deep spending cuts rather than job creation — and little to no discussion of tax hikes — is a fundamentally unserious approach to our economic and fiscal dilemma.

Why do so many Dems continue to capitulate to the right’s austerity/cut-cut-cut frame?

* The House GOP strategy in budget negotiations: GOP leaders may try to ratchet up pressure on Dems to move in their direction by increasing their demands for spending cuts. Imagine if Dems approached negotiations in this fashion...

* Big-picture demographic shifts favor Dems? Though much talk has focused on how new census data shows an increase in House seats in red states, Aaron Blake and Chris Cillizza offer a fascinating look at how the larger population shifts over time may favor the Democratic Party.

Cliff notes version: The country is getting less rural and more diverse, and the areas showing the most population growth are Democratic.

* Wisconsin GOP (alleged) thuggery of the day: A respected historian and critic of Scott Walker alleges that the Wisconsin GOP is trying to retaliate against him by seeking access to his emails via a state open records request. More on this later.

* Another wee problem with Romney’s line on health care: It’s mostly escaped notice, but Mitt’s frequent claim that Federal health reform represents a dreaded “one size fits all” solution being imposed on the states is a very serious distortion in its own right.

* Satire of the day: Glenn Greenwald, in a sendup of the zealous calls for crackdowns on whistleblowers who make our government look bad, calls for urgent investigation into whoever was behind the leak of U.S. classified intelligence designed to serve our public relations aims by showing that Gaddafi forces faked civilian casualties.

* Redefining “pro-Israel”: An interesting write-up of left-leaning J-Street and its quest to redefine what it means to support Israel in defiance of those who insist on unconditional support for everything Israel does.

* And will previous acknowledgment of climate change bedevil 2012 GOP hopefuls? Great stuff from Michael Scherer, who compiles video evidence that many of the 2012 GOP hopefuls once professed agreement with the science of climate change.

Needless to say, this will now force them into all sorts of pandering contortions and flip-flops as they navigate the climate-denying GOP base. Fun times ahead!

What else is happening?