THE ALTERNATIVE UNIVERSE IN WHICH CONGRESS FUNCTIONS…. Sen. Mary Landrieu (D-La.) hopes this week’s special election in Massachusetts serves “as a wake-up call to the wing of the Democratic Party that wants the federal government to overreach and overspend.”

Matt Yglesias’s response reminded me of a point I’ve been meaning to make.

You can easily imagine an alternate universe in which the Senate Democratic Caucus took an oath of party loyalty, that all 60 Democrats would vote for cloture on all leadership-supported bills, allowing measures to pass with just 51 votes. Had that happened, we would have gotten a bigger, more liberal-friendly stimulus. And the Senate would have finished up with a more liberal version of health reform some time ago. And the Senate probably would have passed some other liberal stuff in the meantime. Had that happened, and had the voters been displeased with it, then it might make perfect sense for Landrieu to complain about some non-Landrieu “wing” of the Democratic Party.

But in the world that exists, the only “wing” that matters is the Mary Landrieu wing.

I suspect just about every politically-engaged Democrat in the country has spent a fair amount of time this week lamenting the fact that the party — perhaps more so than at any point in recent memory — seems feckless, ineffective, and weak. “If huge Democratic majorities and a Democratic president can’t deliver on their own agenda, what possible good are they?”

The answer seems like a cop-out, so go ahead and blast me for writing it, but it’s worth emphasizing the alternate universe Matt described. If a majority of the House and a majority of the Senate could approve legislation — if, in other words, Congress could function the way it used to and the way it was designed to — Democrats would have finished an ambitious heath care reform bill months ago. The stimulus would have been bigger and more effective. The prospects for a climate bill and reform of Wall Street would be excellent. The progressive productivity of this Congress would rival that of the New Deal and Great Society eras.

But that’s not the legislative dynamic we’re dealing with. Instead we have unprecedented obstructionism from a right-wing minority, which tries to block voting on literally every bill of any significance — a situation that has never existed before in American history — and a small handful of Senate Democrats — including Mary Landrieu and her “wing” — willing to help them.

The principal hurdle, in other words, standing in the way of the party delivering on its agenda is a dysfunctional system that empowers a small congressional minority to kill the majority’s agenda — and creates an electoral incentive for the minority to do just that.

This has exactly zero resonance with the public, which cares about results, not procedural hurdles. But it’s painful to realize what would be possible — how much change policymakers could deliver — if Congress simply returned to majority rule, the way the institution was intended to operate.

Mary Landrieu, Ben Nelson, Joe Lieberman, Blanche Lincoln, and Evan Bayh could do as they please — they could even vote with Republicans on everything that matters — and no one would suffer because of it. Instead, thanks to indefensible and undemocratic Republican tactics, literally nothing passes without the approval of these center-right Dems.

Dems have every reason to be angry and frustrated, but Dems should also remember who is most deserving of their ire.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.