DENVER — GIVEN all of the smoky talk about Colorado and marijuana, you arrive here with the feeling that you’re stepping into some freaky, one-of-a-kind laboratory.

And you are.

But the experiment goes well beyond the responsible legalization and regulation of pot. It extends to questions of whether drillers and environmentalists can peacefully coexist, whether a country bloodied by gunfire can muster any sane response, whether Democrats can use demographic trends and certain social issues to establish a durable advantage, and whether Republicans can summon the specter of an unwieldy government to prevent that. Colorado is where all of this is being hashed out.

“It’s a test tube, and people keep shaking it,” the state’s governor, John Hickenlooper, said when I remarked that seemingly every big issue finds vivid expression here, and that Colorado has become the nation’s mirror, rocky and stoned. It’s in the news much more often than its size — it’s the 22nd most populous state — gives it any right to be.

It’s pivotal in the battle for control of the United States Senate. Senator Mark Udall, a Colorado Democrat, is up for re-election in November. Republicans smell blood. And the forces shaping the race between him and his opponent, Cory Gardner, are the same ones that are shaping the parties’ national fortunes.