Over the weekend, Mayor Michael Bloomberg of New York announced that he would spend $12 million on ads pressuring a number of Senators in 13 states to support Obama’s gun reforms. The NRA has vowed to respond on the air, meaning the battle over guns will intensify in the states as Congress remains on recess for the next two weeks.

Bloomberg’s ads — which focus largely on the proposal to expand background checks — will target a number of GOP Senators. But the more interesting dimension to this is that they will also target red state Dems: Kay Hagan of North Carolina, Mary Landrieu of Lousiana, Mark Pryor of Arkansas, Joe Donnelly of Indiana, and Heidi Heitkamp of North Dakota.

So where are these red state Dems on expanding background checks?

The last time I checked into this, Pryor’s office refused to respond to the question, while a spokesperson for Landrieu confirmed she had not taken a position. As best as I can determine, Donnelly and Hagan have not taken a clear position. Heitkamp recently took a beating from the gun control forces for describing Obama’s proposals as “extreme,” prompting her to issue a statement declaring that “we have a responsibility to keep guns out of the hands of criminals and the mentally ill, while protecting the rights of law abiding gun owners.” Expanding background checks would do exactly that, but Heitkamp has since been cagey on where she stands on them.

It is crucial that these Democrats show the political courage to stand up for expanded background checks. They are supported by nine in 10 Americans, including 87 percent of Republicans. Failure to embrace expanded background checks will send a signal that public opinion over the proposal is divided and that it is controversial. But opinion is not divided at all. This proposal has universal public support. It is not at all controversial. Even huge majorities of gun owners support the idea. If Democrats can’t win the argument over this — even in red states — what can they win an argument over?

Senator Joe Manchin of West Virginia — who has an “A” rating from the NRA — has endorsed expanded background checks. Even staunch “gun rights” GOP Senator Tom Coburn supports the policy goal of the proposal and is only reluctant to endorse it because of bogus concerns about record keeping on sales. If red state Dems continue to balk, it could reduce the pressure on moderate Republicans to support this overwhelmingly popular policy response to a problem that continues to claim the lives of tens of thousands of Americans each year, including children.

The NRA has historically proven very good at cowing lawmakers by rapidly mobilizing a small but highly impassioned minority to create the impression of broad public outrage about the proposed regulation of firearms. So it’s understandable that Dem lawmakers might be reluctant to embrace something the NRA has opposed. But this time, skittishness simply won’t fly. Democrats are going to have to swallow hard and support what the American people want them to support. Falling short here will be unacceptable, and liberals and Democrats should make that 100 percent clear right now.

* Sequester undermines Obama’s economic agenda: This week Obama will sign the measure that has cleared that House and Senate that would continue funding the government through September at sequestration spending levels. As Zachary Goldbarb points out in a good piece, this is forcing the President to enact exactly the opposite economic agenda from the one he outlined after comfortably winning reelection, i.e., more stimulus spending to create jobs.

This again underscores the degree to which we’re dealing with the hangover from the misguided deficit mania of 2011, which Obama himself helped create. We remain trapped in the wrong conversation.

* The sequester’s state-by-state impact: The Post has a useful interactive graphic that allows you to look at the impact the sequester will have on schools, public health programs, assistance for seniors and other areas in each state. One thing to watch for is whether there is a palpable shift in the politics of the sequester in April. If not, it could mean that officials are proving able to weather whatever backlash is happening, which in turn would make it more likely that we’re stuck with extended sequestration.

* John McCain emerging as key target for background checks: The Hill reports that Democrats are quietly hopeful that John McCain will support the emerging Senate proposal that would expand gun background checks. Two other targets: Senators Susan Collins and Dean Heller. That dovetails with my reporting, too. I would add that discussions with Tom Coburn (whose support would be important given his staunch “gun rights” rep) are not completely dead. Senator Joe Manchin has made him a compromise offer.

The search for one Republican Senator (aside from Mark Kirk) to support a policy backged by 9 in 10 Americans has so far proven fruitless, but there remains an endgame in which the measure garners real bipartisan support.

* SCOTUS set to hear gay marriage cases: With the Supreme Court set to hear the Defense of Marriage Act and Proposition 8 cases this week, Jeffrey Toobin has a very nice piece detailing the underlying legal issues and larger social and political context within which they are unfolding. This is an apt summary:

The two cases present variations on the same fundamental question: Is there any circumstance in which the state can deny gay people benefits that are granted to straight citizens?

As I keep telling you, an expansive ruling declaring Prop 8 unconstitutional could give advocates the tools to topple state laws outlawing gay marriage around the country. But as Toobin notes, the larger story is that full equality nationally is inevitable in the long run, no matter what the court rules.

* Claire McCaskill backs gay marriage: The Missouri Senator comes out for marriage equality, which is notable partly because she represents a conservative state, and previously she had not been willing to take this step. Every little thing that demonstrates that the culture is changing can only help.

Taegan Goddard’s tally: “There are now 42 sitting U.S. Senators who back gay marriage.”

* Obama to push for immigration reform: Today the President will deliver remarks urging immigration reform at a naturalization ceremony from 28 individuals representing 26 countries. Per a White House official: “While the President remains pleased that Congress continues to make progress towards commonsense immigration reform, he believes Congress needs to act quickly and he expects a bill to be introduced as soon as possible.”

Obama has struck a relatively low profile in this battle, probably because getting Republicans to agree to a path to citizenship is already very delicate operation that could be made even harder if his name is attached to it.

* Rand Paul gets it right on pot laws: I’m with John Cole on this: It would be nice to have a better spokesperson here, but at least Rand Paul is willing to say it:

“Look, the last two presidents could conceivably have been put in jail for their drug use, and I really think, you know, look what would have happened, it would have ruined their lives,” Paul added. “They got lucky, but a lot of poor kids, particularly in the inner city, don’t get lucky. They don’t have good attorneys, and they go to jail for these things and I think it’s a big mistake.”

* And GOP party identification plummets: Markos Moulitsas posts a remarkable chart demonstrating that Huff-Pollster.com’s averages have GOP party identification down to 27 percent — the lowest since 2009. What remains to be seen is whether the GOP’s failure to substantively evolve on major policies (despite all the talk of a “makeover”) will exacerbate that trend, and what sort of an impact it will have on the 2014 battle for the House and Senate.

What else?

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.