If supporters of gun reform are going to have any chance at realizing their agenda in the wake of the defeat of Manchin-Toomey, they will have to show that Senators can be made to pay a genuine political price for opposing progress on gun violence.

A new Pew poll sheds light on why this may prove very challenging — but it also has some findings that will lend some comfort to gun safety advocates. The poll finds:

47% express negative feelings about the vote while 39% have a positive reaction to the Senate’s rejection of gun control legislation that included background checks on gun purchases. Overall, 15% say they are angry this legislation was voted down and 32% say they are disappointed. On the other side, 20% say are very happy the legislation was blocked, while 19% say they are relieved.

So more Americans nationally reacted negatively to the vote (47) than positively (39). On the other hand, this is well out of sync with the 90 percent who support expanded background checks, and negligible numbers on either side have intense feelings about the vote — showing, again, that gun violence may not be a motivating issue. I’d caution against reading too much into this, however. Pew’s numbers may be influenced by the use of “gun control” in its question wording, and many recent polls still show overwhelming support for expanding background checks when respondents are asked specifically about this idea. Still, it remains unclear whether there’s any political penalty to be paid for opposing them.

This finding, meanwhile, is key:

In the 13 states where one senator voted in favor and one voted against the bill…the overall balance of opinion is similar: 49% say they are angry or disappointed, 36% very happy or relieved.

And so, even in red or purple states, ones in which Senators voted No (Kelly Ayotte, Max Baucus, Jeff Flake, Rob Portman), significantly more were unhappy about the vote than were happy about it. Gun control advocates still hold out hope that these Senators can be won over, and these numbers will not dim those hopes. On the other hand, they don’t tell us whether an intensity gap persists in these states, in which partisans on the right do more to organize, lobby Senators, and donate money than partisans on the left do, which has historically been the case. This is something  Mike Bloomberg’s Mayors Against Illegal Guns — and liberal groups — are hoping to change by building a long term pressure infrastructure.

In a very interesting experiment along these lines, Ron Fournier reports that Mayors Against Illegal Guns is seriously considering a months long advertising campaign pressuring the Arkansas Senator to drop his opposition to expanding background checks. No doubt Pryor would scoff at pressure from a New York billionaire, but the campaign may focus on Dem base voters, such as African Americans, and possibly also suburbanites.

The campaign would function as a test case as to whether partisans on the left can be energized and engaged around the gun issue in a sustained way, as they are on the right. Gun control advocates need to show that Dems can be made to pay a genuine political price for opposing gun reforms that enjoy near-universal support (despite the fact that guns are not a motivating issue), even in a red state.

* Liberals push Brian Schweitzer to run in Montana: Sources close to former Montana governor Brian Schweitzer say he’s leaning toward running for the seat of retiring Max Baucus. The Progressive Change Campaign Committee is already gearing up with a Draft Schweitzer movement, on the grounds that he is “a bold progressive populist who supports single-payer health care.” The PCCC tells me:

Since yesterday afternoon, over 13,000 people joined the Progressive Change Campaign Committee’s DraftBrianSchweitzer.com campaign, and have donated over $17,500 to a Draft Fund which will go to Schweitzer on Day One of his U.S. Senate campaign in Montana.

This is partly driven by progressive relief at the retirement of Baucus, who has steadily voted against the Dem leadership, dragged his feet legislatively in a way that helped embolden opponents of Obamacare, and has a whole constellation of former aides working as lobbyists.

* Good riddance to Max Baucus: Must read: Matt Miller gives the Senator the sendoff he truly deserves, and details all the ways in which the possible ascension of Schweitzer to the Senate, and of Ron Wyden to the Finance Committee chairmanship, offer genuinely bright prospects for our future:

Never has a politician done so much to lift the prospects of the republic simply by saying goodbye.

Ouch.

* How the Boston brothers allegedly built their bombs: This was previously suspected, but it’s now been confirmed:

When Dzhokhar Tsarnaev spoke to investigators on Sunday, officials said, he indicated that he and his brother had learned to make the pressure-cooker bombs that they used at the marathon from Inspire, the online Al Qaeda magazine.

Thus far, however, no evidence has emerged of any contact between the brothers and Al Qaeda or any affiliates.

* Where the brothers got their bomb materials: It’s now emerged that Tamerlan Tsarnaev allegedly got the black powder for one pressure cooker gun from fireworks he bought at a fireworks store in New Hampshire — and, eerily, it turns out it was the same store where the Times Square bomber bough firecrackers for his failed bombing scheme.

Still outstanding: Where did the brothers get the guns? CNN reported that they got them “elsewhere,” which doesn’t tell us much, but it looks like Tamerlan ventured outside of Massachusetts to get bomb materials.

* A motive for the bombing? The Post reports:

The injured suspect in the Boston Marathon bombings has told interrogators that he and his brother were driven by hard-line Islamist views and anger over the U.S. wars in Afghanistan and Iraq but had no ties to foreign militant groups, U.S. officials said Tuesday.

The timing here is curious, since the wars are winding down. One has to wonder whether the drone program abroad — which obviously remains very active — was a motivator, and if that does emerge, how that scrambles the politics around drones.

* White House wooing Republicans for Grand Bargain? Politico reports that White House officials are quietly reaching out to Republican Senators in hopes of wooing them for a deal on taxes and entitlements. At risk of stating the obvious, no deal is ever going to happen, as long as the GOP remains militantly opposed to any new revenues from the rich.

* Please stop with the LBJ comparisons: Jonathan Bernstein has a nice piece detailing all the glaring historical and logical flaws in yesterday’s big New York Times story claiming Obama is not twisting enough arms, the way LBJ did. Just stop this already. Thanks in advance.

* And a curious approach to rehabilitating George W. Bush: Like Steve Benen, I find this argument deeply bizarre: Bush kept the nation safe since the September 11th attacks, something Obama has failed to do.

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.