Dana Milbank calls this the “Tea Party of the left,” but that’s not quite correct. Politically, the Tea Party grassroots couldn’t be more different than their progressive counterparts in the Democratic Party. One wants the federal government constrained in favor of individual and local prerogative, while the other wants to expand federal power to trump individual and local prerogative. Even the populism that runs through both movements comes from polar-opposite approaches.

The only real similarity comes in the impact of grassroots movements after catastrophic losses — and here, Milbank’s equivalency rings more true:

I pulled aside Pica, water dripping from his nose, to ask whether he really believed that it would be better for the environmentalist cause if Republican House member Bill Cassidy — who says he isn’t even sure climate change exists — wins the runoff against Landrieu, the top Democrat on the Senate Energy Committee.

“Yeah, I think it would be good thing,” the activist said. “Even if it’s a freshman junior senator from Louisiana who’s a Republican, it ends up being better for our issues because you don’t have a leader in the Senate on energy issues fighting for more oil pipelines.”

In fact, Pica wasn’t troubled that so many moderate Democrats with “wishy-washy positions on oil and gas” lost their seats this month. He said a smaller group of uniformly liberal Democrats would help his cause, “particularly as the president is trying to push through executive orders. Having a more united Democratic caucus helps.”

I’ve heard this argument before, coming from tea party activists who said that they would rather have a smaller but reliably conservative caucus than a large majority full of RINOs — Republicans in Name Only — who aren’t reliable votes. The emerging purists on the left aren’t nearly as strong as the tea party was (and they won’t be, as long as there’s a Democrat in the White House), but it’s noteworthy that Democrats are becoming more willing to purge those who aren’t ideologically pure.

This sounds familiar, doesn’t it? It’s the old I’d rather have 30 true believers in the Senate than 70 seats in the caucus routine, which sounds great as a rallying cry. As a strategy for policy influence, though, it’s a stinker. The Tea Party, to its credit, understood this almost immediately, and especially after watching Harry Reid pick up seats in the 2012 election. Majorities matter in both chambers, while minorities get to talk a lot but do almost nothing.

Will progressives learn the same lesson? Perhaps, and Milbank’s trip to an anti-Landrieu rally may not mean all that much. The difference between 53 seats and 54 seats is almost meaningless, except that 54 seats give Republicans better odds of keeping control of the Senate in 2016. But that would presume that Landrieu has a chance in this run-off election and that the protest puts the outcome of the election in danger. That’s so obviously not the case that even establishment Democratic organizations aren’t bothering to spend money in Louisiana for the runoff. Independent pollsters have yet to publish a single survey of the Senate race, despite it being literally the only game left on the schedule.

In other words, there’s no risk here. Progressives can come to Louisiana to burnish their grassroots credentials (and conduct fundraisers) while doing no real strategic damage to Democrats. It gives the progressive grassroots an opportunity to talk tough to the party establishment, but without becoming an actual threat. The real test will be whether these same progressives line up to challenge Democratic incumbents in 2016 like Harry Reid, Michael Bennet, or maybe Barbara Mikulski if she doesn’t retire first. The conditions are ripe for a grassroots-led purity purge — crippling electoral defeat, incompetent leadership, failing agenda — but the question will be whether the P Party has the clout or the nerve to pull it off.