In its primary on Tuesday, Nevada set the stage for the ultimate test of what voters can tolerate least — Democratic incumbents or right-of-mainstream upstarts. The national conversation about immigration — one that had been marginalized nationally and avoided in Washington — has been restarted, and reframed, in Arizona over the last month.

The marriage of the region’s political volatility and its historical relationship to some of the toughest issues being pondered nationwide — immigration, natural resources and energy, the appropriate reach of federal government — have made it a mirror held up to the current political psyche.

Tea Party? Nevada has that movement’s most quintessential candidate in a Senate contender, Sharron Angle, and an equally symbolic opponent in the Senate majority leader, Harry Reid.

As with any exciting stew, the rise of the West’s role in the national political consciousness features many ingredients: history, demographics, physical landscape and local economies.

Yet the region has been and remains less fixed in its political traditions than broad regional swaths elsewhere in America. It has many nonpartisan mayors and city managers, and legislatures often take a back seat to direct democracy through ballot initiatives. It generally lacks strong unions that direct races. Nevada, New Mexico and Colorado are true swing states now.

In recent years, Democrats and Republicans have sought to lock up the West for their parties to better ensure their own power in presidential elections. The opening for both parties to woo new voters in the region stems in large part from demographics and migration. From 2000 to 2010, the population of Nevada grew 32 percent, according to census figures, largely in the southern half of the state. Arizona grew 28 percent and Colorado, 17 percent, still twice the national average for that time period.

“Democrats figured they have lost the South so they need the West,” said Jon Ralston, a veteran political columnist for The Las Vegas Sun. “Reid changed the voter registration numbers even beyond what his wildest dreams were.”

But the rural north of the state remains a conservative stronghold, and the state’s politically libertarian culture is offended by the Obama administration’s spending programs.

If Americans are paying more attention to the West, it may be because many issues on their minds have been pondered here for decades. A position on Arizona’s new immigration law, which requires the police to ask about the immigration status of people stopped for violations of the law, has become the litmus test among many G.O.P. primary candidates.

How long the West will maintain dominance in the political conversation is a matter of some debate. Much of the argument centers on immigration and the economy. Over the last two years, population growth in Arizona and Nevada — migration from other states as well as illegal immigration — has slowed greatly, largely because the dominant industries, construction and tourism, have collapsed.

Hispanics constitute more than 25 percent of the population of Arizona, Nevada and California, according to the Pew Hispanic Center. While they have low voter participation relative to other residents of those states, their potential power is not lost on either party. Republicans have been split over the Arizona law largely because they do not want to alienate Latinos.

“One of the big questions in this state is, ‘Are you going to be able to see the voting intensity among Hispanics that you saw in 2008?’ ” said Mr. Ralston of Nevada, who pointed to the eight Hispanic legislative contenders in his state, all favored to win.“