With oral arguments before the Supreme Court concluded, backers of Obama’s signature domestic achievement are beginning to contemplate the unthinkable: The possible demise of the most ambitious liberal reform since the 1960s, one that was supposed to take its place alongside Medicare and Social Security as a defining achievement of the Democratic Party.

As Amy Gardner details this morning, Dems are beginning to ask whether there would be some political upside if the law is struck down, perhaps a rallying of the base:

“If they overturn the individual mandate and undermine the central element of this bill a few months before the election, it will anger Democrats and rile up the base,” said Neera Tanden, president of the left-leaning policy group Center for American Progress and a policy adviser to Obama’s 2008 campaign. “People will see it for what it is: an activist court rendering a partisan decision.”

A group formed to defend the law, Protect Your Care, is even planning to launch a campaign against the Supreme Court, one targeting seniors and young people who would lose big if the law is struck down:

“Since Bush v. Gore, from the progressive side, it would be the most galvanizing Supreme Court ruling ever,” said Eddie Vale, a spokesman for the group. “You’d have a 5-4 court, in clearly a partisan political decision, striking down not just President Obama’s biggest legislative accomplishment but also the biggest progressive legislation since LBJ.”

It’s impossible to predict the politics of a loss at the Supreme Court. I tend to doubt that it’s a positive for Dems in any way. In any case, it’s premature to assume a loss.

But if we’re going to discuss the politics of this possibility, surely the demise of Obamacare — which Republicans have been agitating for since even before it became law — should put pressure on Republicans to say what they would do instead.

So: When is the fact that Republicans would replace Obamacare’s most important provisions with nothing meaningful in the way of a solution to the problem of the uninsured going to become a part of the media narrative?

Both Mitch McConnell and Mitt Romney have basically confirmed that if Obamacare is repealed, they would effectively replace it with ... nothing, particularly when it comes to those with preexisting conditions. Yet as Jason Linkins points out, in Romney’s case it was left to Jay Leno, of all people, to reveal this for all to see. You’d think more news orgs and commentators would at some point begin to grapple with the fact that the other major party isn’t offering anything meaningful to deal with one of the nation’s most pressing problems. This seems tangentially important, now that the destruction of the Dem effort to solve it is a real possibility.

* Killing Obamacare would kill our “obligation” to one another: E.J. Dionne reckons with the fact that the other party is offering nothing as an alternative to Obamacare, and explains what that means:

When Solicitor General Donald Verrilli explained that “we’ve obligated ourselves so that people get health care,” Scalia replied coolly: “Well, don’t obligate yourself to that.” Does this mean letting Butler’s uninsured guy die?

Slate’s Dahlia Lithwick called attention to this exchange and was eloquent in describing its meaning. “This case isn’t so much about freedom from government-mandated broccoli or gyms,” Lithwick wrote. “It’s about freedom from our obligations to one another . . . the freedom to ignore the injured” and to “walk away from those in peril.”

This is what conservative justices will do if they strike down or cripple the health-care law.

* Here’s another “limiting principle” for you: In a good piece rebuffing all the conservative legal arguments against Obamacare, David Cole identifies another one:

To uphold this law would not give Congress unfettered power to require us to eat granola, purchase electric cars or join health clubs. Participation in the markets for those products is not inevitable, nor does one person’s choice not to purchase such products impose substantial and foreseeable costs on others because he will be able to get the product for free even if he doesn’t buy it. Upholding the individual mandate would simply establish that where a national market is the victim of such a free-rider problem, Congress may address it as part of its general authority to regulate that market.

Former Reagan Solicitor General Charles Fried agrees.

* It’s up to the Court to come up with its own limiting principle: Kevin Drum on how it’s up to the Supreme Court Justices themselves to figure out that the individual mandate doesn’t empower government to force-feed you broccoli.

* Obama making gains among key groups: The new CNN poll finding Obama leading Romney among registered voters by 54-43 also includes this:

“President Obama currently wins majority support among groups that have been problematic for him in the past, including men, older voters, and suburbanites. He has a solid lead among independents as well.”

Romney’s favorability rating among independents is a dismal 35 percent, perhaps a reflection of the toll of the primary, but I continue to think he’ll have another chance to reintroduce himself to core swing constituencies on more favorable terms once he’s the nominee.

* Ban on outside ads working in Massachusetts: Dan Eggen brings the good news: The agreement Elizabeth Warren and Scott Brown reached to bar outside spending appears to be holding.

This must be awfully frustrating for groups like the Rove-founded Crossroads GPS, which previously had spent hundreds of thousands of dollars flooding Massachusetts with ads painting Warren alternately as a tool of Occupy Wall Street and a stooge for the big banks

* Sherrod Brown comfortably ahead in Ohio: A new Quinnipiac poll finds Sherrod Brown leading challenger Josh Mandel by 10 points, 46-36. Outside right wing groups have poured more money into this contest than into any other Senate race, because both sides are banking on it to tighten considerably, and for all the attention to Massachusetts, Ohio has quietly emerged as central to Dem hopes of holding the Senate.

* Trayvon shooting highlights political realities hiding in plain sight: Gail Collins: “Whenever there is a terrible shooting incident somewhere in America, our politicians talk about everything except whether the tragedy could have been avoided if the gunman had not been allowed to carry a firearm.”

* Romney as Goldwater? An intriguing suggestion from Michael Hirsh: Could Romney’s warmongering rhetoric and empty chest thumping towards Iran and Russia turn him into Goldwater circa 1964, at a time when Americans are weary of war abroad?

* And about that Romney’s “humorous” story about layoffs: Steve Benen has the audio, and points out that this illustrates yet again that Romney is simply incapable of discussing wealth and power in public.

What else?