Republicans stuck in an 'electoral cul-de-sac?' That's how it looks near Denver

"I'm pro-Hillary and anti-Trump," says Patti Dubé, whose husband is of Canadian heritage. 

"My decision is to vote for Hillary," says Kimberly Thebeau. 

• Trump's Deep South diehards ready for revolt if he loses
• Clinton's email controversy opens up fuzzy world of document secrecy

In two hours, all except one of those 20 or so voters said they picked Clinton, the Democratic candidate locked in a battle with Republican presidential hopeful Donald Trump.

For Republicans, this is bad news. Really bad. Because what's happening here is slowly happening in suburbs across the United States.

Twenty years ago, Colorado was a red state. And this suburb of Arapahoe County just half an hour outside Denver was just as Republican as the rural outskirts. 

More diversity

"The southern ring counties in Colorado used to be the most conservative in the state," says Tony Robinson, political science chair at the University of Colorado Denver.

"In the last two election cycles, Arapahoe County has voted Republican at the presidential level."

• Why Donald Trump's path to win Pennsylvania runs uphill
• More stories and analysis on the U.S. presidential election

So what happened?

First, Colorado started becoming younger, more educated and more diverse. It began in Denver, then the ripple slowly spread.

"They're moving into the suburbs," says Robinson, "and when they do they change those voting patterns. And the suburbs are no longer reliably red."

Fifteen years ago, Charles Twitty was the only person of colour in his neighbourhood. Not anymore.

"Colorado, especially Arapahoe County, is becoming a melting pot," he says as he drops off his vote for Clinton at the ballot box.

• Is Clinton the only 'adult' or 'beyond the law?' In Ohio, it depends where you ask
• Eric Grenier's Poll Tracker: See what the numbers are saying
• What's at stake in this U.S. election

The problem is, Robinson says, the Republicans' message doesn't appeal to these new suburban voters.

"Donald Trump represents the old notion, that kind of old, white, male voters are the centre of American politics, and he is speaking to them. And that once was true in a county like Arapaho County. It is no longer true."

Some Colorado politicians are trying to adapt. Mike Coffman, the Republican congressman who represents Arapahoe County, cut an ad dumping on Trump.

Latinos aren't buying it

"Honestly," he says in the ad, "I don't care for him much."

Then Coffman released an ad in Spanish.

But Arapahoe County resident Luiz Castillo says most Latinos he knows aren't buying it and they're coming out in droves to vote for Democrats.

"This year they know it's very important for them," Castillo says. "They know that we get very affected if we don't go out there and vote."

These demographic changes aren't just happening in Colorado. Robinson says there's a similar pattern in Georgia, Virginia and Pennsylvania. 

And Colorado's demographic transition, he says, "is leading the way that America is changing in general."

The other reason Trump signs here are a rare sight: Republican candidates have become too right wing for many suburban Republicans.

Matthew Dionne says the party expects him to vote for these more extreme Republicans simply out of party loyalty.

"We're being dragged kicking and screaming to vote for whatever candidate they've dragged forward for us."

Now, for the first time, he says he's not voting Republican. 

And these trends are bigger than Trump.

Robinson says identification with the Republican party in Colorado has gone down five per cent in the last 10 years. Across the U.S., the Republicans have lost most major urban areas.

"The Republican party right now is in an electoral cul-de-sac," Robinson says. "A dead end. Any party that is continuing to build its base on 70 per cent of its voters as white males has no future."

The electoral math may come down to this equation: win back Arapahoe County, win back the White House.

• How a U.S. president is elected