No one talks about this openly, but it is being privately discussed at the highest echelons of the Democratic Party. Let’s say the Toomey-Manchin compromise on expanded background checks goes down in the vote that’s scheduled on it today, and whatever package ultimately passes is essentially a joke. What happens if and when there are more shootings down the road?

By all indications, Manchin-Toomey appears to be dead. Senators Dean Heller and Lisa Murkowski — the last Republicans thought to be gettable — came out against the proposal last night. Even if all the wavering red state Dem Senators — some of whom still remain undecided — vote Yes, there’s no clear route to 60 votes, given that only four Republicans appear prepared to vote for it. Even Senator Manchin himself conceded this morning that the proposal doesn’t have the votes.

Here is the situation some of these Senators — red state Democrats and purple state Republicans alike — may well find themselves in before long: There may well be another horrific shooting, and they will be on record voting against common sense proposals to stem gun violence, ones supported by an overwhelming majority of Americans.

By the way, I’m not just talking about mass shootings here. I’m also talking about gun murders that don’t receive national attention but could occur in states whose Senators voted against expanding background checks — and could have been prevented by a better background check system. Killings such as the one documented by the New York Times today.

There’s a whole history here that bears this out: Congress has repeatedly been spurred by shootings to act on proposals that originated in the wake of previous shootings. It has repeatedly taken years to pass gun control legislation. The Gun Control Act of 1968 passed in the wake of the assassinations of Martin Luther King and Robert Kennedy, but it originated in the wake of the assassination of JFK five years earlier. The Brady Law passed in 1993, many years after the shooting of Jim Brady. Six years later still, after the 1999 Columbine massacre, the Senate passed a bill closing the loophole in the law (it failed in the House).

If Manchin-Toomey dies, there will a lot of chatter to the effect that the chance for action is now gone for good. And it’s true that the Newtown shooting, because of its particularly horrific nature, did seem to create circumstances for action that had long been lacking. But the history of gun control tells us this is sometimes a long game.

If Manchin-Toomey dies, there also will be a lot of chatter to the effect that this was inevitable, that the NRA’s grip on Congress is invincible, and that it was naïve to imagine that anything could happen, even after Newtown. This is all just wrong, and indeed, it lets culpable Senators off the hook. If the proposal goes down, it will be because a few Senators did the wrong thing. It was not at all inevitable that a half dozen Senators who were genuinely undecided voted one way and not the other. The death of this proposal will be on them.

Whatever the prospects for future gun reform, it is all but certain that Senators who vote No today will eventually be confronted by another shooting — whether it’s a particularly gristly murder in their state or a high profile massacre that gets national attention. And they will be unable to say they did something to try to slow the carnage when they had the chance. Is that what they really want?

* The free-for-all of online gun sales: The New York Times weighs in with yet another excellent investigation on the gun issue, this one documenting that thousands and thousands of guns are sold online in what essentially function as “unregulated bazaars” where felons buy from unlicensed sellers. This is key:

The examination of Armslist raised questions about whether many sellers are essentially functioning as unlicensed firearms dealers, in contravention of federal law. The law says that people who “engage in the business” of selling firearms need to obtain a license and conduct background checks on customers. While the definition of engaging in business is vague, The Times found that more than two dozen people had posted more than 20 different guns for sale in a several-month span.

Those who like to argue that Manchin-Toomey wouldn’t reduce crime need to be asked: Don’t you view this as a problem worth addressing?

* Today is do-or-die for background checks: Senator Richard Durbin, the Democratic whip, tells reporters that there is no fallback plan to introduce a modified version of Manchin-Toomey if it fails today. That means today’s vote is very likely the last chance to expand background checks for the near future.

* John McCain, a voice of sanity on guns: The Post has a good editorial today hailing Senator McCain’s sane approach to the issue of background checks, and urging other Senators to follow suit. It’s still hard to believe that a few red state Dems would still oppose this, even with the cover afforded them by not just McCain, but also Pat Toomey and Joe Manchin, both of whom enjoy “A” ratings from the NRA.

* Dean Heller’s laughably weak argument on guns: Senator Heller initially seemed gettable on Manchin-Toomey, but as Steve Benen’s dissection of Heller’s ridiculous and dishonest rationale for voting against it demonstrates, he was never actually serious about doing anything meaningful about gun violence.

* Senators make up fake excuses to vote No on Toomey-Manchin: Relatedly, David Firestone gets this exactly right: Senators such as Jeff Flake who are voting against expanding background checks are simply making up fantasy rationales for their vote. What this confirms, again, is that opponents of the proposal have no arguments against it without lying about it.

* Marco Rubio angers right on immigration: The Washington Examiner’s Conn Carroll argues that the enforcement triggers necessary to set in motion a path to citizenship in the new immigration deal reached by the Gang of Eight falls well short of what Senator Rubio previously insisted was his bottom line. The question is whether Rubio will face any meaningful backlash from conservatives after widely promising them that he’d negotiate a tough enforcement provision, and what that would mean for his 2016 hopes.

* And foes of immigration reform plan delaying tactics: The Post reports that conservatives are plotting a careful strategy designed to kill immigration reform with procedural delaying tactics and poison pill amendments. The strategy — which represents a gamble that the coalition behind reform is so fragile that it can be divided with skillfully chosen amendments — is a reminder of the right’s determination not to let the GOP evolve along with demographic and political realities.

Also check out the Post’s handy chart breaking down what the immigration reform proposal does.

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.