For all the decades of its existence, American social conservatism has been rooted in a premise simple enough to be fully expressed in just three words:

Us versus them.

As in, an implicit promise to defend the former against the latter. This was its mission when it pushed for immigration quotas in the 1920s, when it animated the Red Scare of the 1950s, when it defined civil rights as a clear and present danger in the 1960s, when hardhats rioted against hippies in 1970. It is its organizing principle even today, as red states pass legislation to protect themselves from Sharia law and some of us define religious persecution as baking a cake for a same-sex couple.

Us versus them.

Always, social conservatism defined “them” as something faceless and frightening against which the rest of “us” must struggle with everything we had, or else be overrun. It is an ideology that has contributed virtually nothing of value to the life of the nation — unless you count mindless panic as a good thing.

So one is gladdened by signs of its decline.

There have been many signs in recent years, but one of the most compelling is found in a new Gallup survey. According to the polling company, just 31 percent of all Americans now identify themselves as social conservatives. That’s the lowest number in the 16 years Gallup has been tracking that question. It also marks the first time social liberalism has pulled even: 31 percent of Americans now identify with that ideology. For social conservatives, the decline has been precipitous: As recently as 2009, their share of the electorate was 42 percent.

And here, let us reiterate what we are not talking about. We are not talking about fiscal conservatism, which seeks to rein in government spending. We are not talking about foreign policy conservatism, which demands that America deal with its opponents from a position of toughness and strength. Nor are we talking about small government conservatism, which considers Washington a maze of needless regulation and oversight.

Each of those ideologies has its virtues and failings, but today we are talking about the conservatism of us versus them.

One suspects it has been, in some sense, a victim of its own success. Social conservatism’s attraction has always lain in its appeal to simplicity. It says: Forget nuance, complexity and all the historical, political and socio-economic realities that make the world what it is. Forget compassion and the burden of shared humanity. Those people over there are the cause of all your troubles. That tribe is the one you should fear.

Such thinking has always enjoyed a measure of acceptability. It probably always will; for some of us, it is intellectual comfort food. But in recent years, that ideology has risen to a high water of visibility and political potency it has not enjoyed since the 1950s. The unintended byproduct is that we have been able to see very clearly what that rhetoric looks like in practice.

Turns out it looks like the outlawing of ethnic studies classes. And restrictions on contraceptives. And demonized Muslims. And scapegoated gay people. And the erosion of civil rights. And guns everywhere. Turns out it looks like an Arizona state lawmaker who wants to make church mandatory.

Gallup’s numbers suggest more Americans are seeing through this con job, this appeal to their basest selves. They suggest the GOP, held in willing thrall to this thinking for years, may now have a chance to break free. If the numbers continue in this direction, it may have no other choice.

Or so we should fervently hope. We know, after all, through bitter experience what happens when you pit us against them.

Nobody wins.

Leonard Pitts is a columnist for The Miami Herald, 1 Herald Plaza, Miami, Fla., 33132. E-mail him at lpitts@miamiherald.com.