— The road to victory in many of the most competitive states in this year’s presidential election winds through the strip malls, traffic jams, limping economies and slumped housing markets of the suburbs.

Nowhere is the trend more pronounced than in Colorado, where two counties near Denver — Jefferson and Arapahoe — have become a central focus for both campaigns. Once reliably Republican, these suburban counties have grown more diverse and less partisan — and home to the largest concentration of the unaffiliated voters widely expected to decide the election.

The likely prize for the campaign that succeeds in reaching these voters is the entire state and, in a razor-thin national contest, perhaps even the election.

“You show me who wins Arapahoe and Jefferson counties and I’ll show you not only who wins Colorado,” said Eric Sondermann, a nonpartisan political consultant in Denver, “I’ll show you who's sitting in the Oval Office next January.”

That thinking helps explain why President Obama will make a campaign appearance in Golden on Thursday morning, his ninth visit to Colorado this year. It explains why Republican Mitt Romney has touched down in the state six times in 2012 and why one of his sons, Josh Romney, addressed a “Young Americans for Romney” gathering in Arapahoe on Wednesday night. And it explains the clutter of television and direct-mail advertising filling the living rooms and mailboxes of coveted undecided voters here.

Population growth is the single biggest reason why the political dynamics of these suburbs have changed. Arapahoe County’s population has doubled since 1980 to nearly 600,000; Jefferson’s growth rate is not far behind. Together, they are home to nearly one-quarter of Colorado’s electorate, making the state among the most suburban in the country.

Who has moved in is just as important. Educated young professionals with Latino, Indian and Chinese surnames have become commonplace on the voter rolls. Mountainside mansions coexist with more modest neighborhoods. Yoga studios and REI stores (there are five in the Denver area alone) sit alongside Home Depots and Wal-Marts and, in Golden, the sprawling headquarters of Coors Brewing.

The newcomers have brought new politics with them. Suburbs once known for their Main Street Republicans are equally populated now by a broader mix of less partisan, more pragmatic voters who prefer to think of themselves as independent. They vote on the issues they see affecting them, such as school quality and the fate of the economy. Even the pro-business Republicans in many cases lean independent, according to public polling, because of what they see as the increasingly conservative and ideological message of the Republican Party.

“When I first came here I felt very much like I was an alien,” said Ginny Lee, 50, an information technology worker and registered Democrat who moved to Golden in the 1990s from California, and whose grandparents are from China. “Part of feeling more comfortable is that I’ve changed, but part of that is the community changing too.”

The new pragmatism explains why Romney has tried to focus exclusively on the economy in Colorado, as he has most everywhere else. His ads contend that Obama’s policies have left Coloradans no better off than they were four years ago, and they blame Obama’s regulatory initiatives for worsening the business climate. Romney’s campaign here pushes out statistics on Colorado’s real-estate market (eighth-highest foreclosure rate in the nation) and its unemployment rate (above the national average).

“The undecided voters are concerned about what’s going on in the country,” said James Garcia, Romney’s Colorado state director. “They’re concerned about the economy; they’re concerned about the unemployment rate. Every single person we talk to, whether they’re Republican, unaffiliated or Democrat, their concern is how they’re going to put food on the table.”

For Obama, who won Colorado four years ago by nearly nine percentage points, the focus has been heavily on Latinos and women. One of the quirks of the new unaffiliated voters who have moved into suburbs across the country — including in other battlegrounds such as Virginia and North Carolina — is that the men who describe themselves this way tend to vote Republican, according to polls, while the women are more likely to swing between the parties.

Just as non-ideological as their male counterparts, unaffiliated women voters are also particularly moved by issues that affect them, such as contraception and abortion. The proof came two years ago, when Sen. Michael Bennet (D-Colo.) eked out a narrow victory over Republican Ken Buck largely by targeting women in the suburbs and portraying Buck as ideologically extreme.

“We created the largest gender gap in the country,” said Guy Cecil, who was Bennet’s campaign manager and now runs the Democratic Senatorial Campaign Committee. “The suburbs of Virginia, the suburbs of Indianapolis, the suburbs of Denver — you have people who are turned off by the sort of extreme points of view that now represent most of the Republican Party.”

Obama is following a similar playbook. He has focused relentlessly on the statements of his opponents — not just Romney but also his running mate, Rep. Paul Ryan of Wisconsin — supporting cuts to Planned Parenthood’s funding or opposing abortion, even in cases of rape or incest. In one of his ads, a woman calls Romney “dangerous” for women’s health.

The Romney campaign, too, is targeting women, featuring a woman in an ad speaking about her economic plight during the Obama years. Both campaigns are also reaching out to Latinos. And through it all, they’re not ignoring their bases, with plenty of outreach happening in the conservative rural areas and Democratic cities, because the election is expected to be close. Obama has opened 54 field offices in Colorado and Romney 14.

“An election like this is good for democracy,” said Colorado Gov. John Hickenlooper (D), a regular surrogate for Obama. “It tells everyone that their vote matters. Both the partisan folks, because you’ve got to get out your base, but also independents, because it’s going to come down quite possibly to 2,000 votes.”