You'll know the gun control movement is winning when...

The organizers behind this past weekend's rallies for gun reform understood this. They made a point of harping on the distinction, making it one of the prevailing rhetorical themes of the demonstrations, which flooded Washington on Saturday and clogged thoroughfares in dozens of other major cities across the US and around the world.

But acknowledging the difference, and pushing for sustained direct action, is only a start. Envisioning a finish is more difficult, especially when it comes to such a politically intractable issue. The question now for the movement: What does winning really look like?

Among the most vocal post-Parkland gun control activists, many of them teens and young millennials, there is an intrinsic understanding that public opinion alone is not a driver of legislative change. They grew up in a cycle where mass shootings -- typically of white people, by white people, in affluent areas -- temporarily jacked up interest, setting off doomed efforts to tighten gun laws, followed by abrupt returns to the status quo ante.

On the fundamental question, poll numbers have almost always been on the young activists' side. Americans generally support tougher gun laws. But those surveys measure sentiment and sentiment, as we've seen over the years, cannot adequately fuel and sustain the kind of disciplined, strategic grassroots work required to alter specific policies and change underlying -- and deep-seated -- political dynamics.

Successful progressive pressure campaigns, no matter their cause, share a handful of distinguishing characteristics.

Among them are a willingness to name enemies and, as importantly, demand more of would-be allies in office -- in the same way, to give a recent example, liberal activists pressured Democrats, even those facing reelection challenges in red states, to maintain the party line in the fight to save Obamacare.

If this weekend marked a breakthrough, perhaps the best symbol was the increased militancy -- in their speeches, on their signs, etc. -- of the demonstrators. The NRA and its elected allies, of course, took their lumps, but in an encouraging shift for activists, so too did individuals who prioritize gun rights over the potential upside to tightening restrictions. It's easy to yell about the gun lobby; it's much more difficult to condemn your neighbor.

The NRA is taking note of the shift. In a tweet on Friday, less than 24 hours before the marches kicked off, the group linked to a blog post titled, "The Stigmatization Of Gun Owners," then added: "The idea is to shift public opinion to such a point that something once socially acceptable -- owning a gun -- is now socially unacceptable."

Well, yeah.

The NRA, which is good at politics (and not just, as some critics suggest, paying off politicians), understands why this kind of "shift" in social norms would be so damaging to its interests. Hence their effort to stigmatize not just the message, but the desired strategic outcome. That most protesters this weekend would've happily endorsed the tweet, and the goal it decries, is yet another green shoot for the movement.

But there are two more crucial pieces that continue to stand between the movement and a clearer path to achieving its aims.

First, we have yet to see consistent signs that gun control supporters are prepared to prioritize the issue, like their opponents do, on election day. A Pew Research Center report from last November underlined the enthusiasm gap with its finding that "Americans who believe gun laws should be less strict are more likely to contact public officials on the issue than those who think gun laws should be stricter or are about right."

If real reform is going to be possible, that will have to change. And if it does, the second step might become more feasible: the election of federal lawmakers, en masse, who campaign on platforms demanding legislative action. We've seen some shifts in this direction on the state level and among entrenched congressional Democrats.

Virginia Gov. Ralph Northam, though running for an executive job, trumpeted his "F" rating by the NRA. In a Washington Post op-ed published after Northam's victory last year, pollsters for his campaign argued that it was "time to rethink a long-held political axiom: Democrats lose when they campaign on stronger gun laws." This past weekend, Georgia Rep. John Lewis drew some headlines by declaring he was "proud to wear that 'F.'"

There are tougher tests up ahead. If Democrats retake Congress and the White House, would they be willing to spend the required political capital to pass new gun laws? The answer, for now at least, is probably not. There are more galvanizing priorities, like expanding public health care programs or access to higher education, that would almost surely come first.

Absent those levels of urgency, and a sense among enough lawmakers that actively supporting new restrictions is a pragmatic requirement, one they'll be confident defending in the next campaign, action is unlikely. But even that might not be enough. The issue is too simply too hot. The backlash is inevitable and, for politicians, unavoidable. Ultimately, something more will be required.

If the gun control movement is going to win, it must find allies in government willing to lose.