Visits to the competing campaign headquarters and satellite offices provide instant proof of the urgent emphasis on turnout - the so-called ground game, including nudging less reliable voters to take advantage of Colorado's early voting window, which opens October 22.

"We are, I believe, at ground zero in the presidential election," is the view of veteran Democratic strategist Michael Stratton.

Heading into the final four weeks, Stratton said Colorado is again up for grabs -- and a new University of Denver poll released this past weekend backs that up.

In the survey, Obama received 47% support to 43% for Romney. Just shy of six in 10 Coloradans said the economy was the top issue, and they gave Romney a slight edge (50%-to 45%) when asked which candidate would do a better job on the economy.

"Before the concept of red and blue, before the concept of purple, you remember they called Colorado a ticket splitter state," Stratton said in a coffee shop interview across the street from his Denver office.

Bill Clinton won Colorado in 1992, but lost it in 1996. George W. Bush carried it twice, but never with more than 52% of the vote. Then Obama returned Colorado to the blue column in 2008, winning rather comfortably with 54%.

Since then, however, unemployment in the state has risen a bit, from 7.2% when Obama took office to 8.2% now. In the University of Denver poll, 23% of Coloradans said their personal economic situation had improved over the past year, 41% said it has stayed the same, and 36% said it was worse.

In addition to evangelicals, Stratton said Romney can safely count on deep support from the state's Mormon voters - like Romney members of the Church of Jesus Christ of Latter Day Saints.

"In some places, as you know, there are concerns about Mormonism," Stratton said. "People here all know Mormons. They are family people. You won't hear as in some parts of the country, 'who are these people? Are they some weird cult or something?' ... The Mormon thing helps him here."

The keys for the president, he said, are healthy turnout among Latinos and a heavy focus on suburban women.

On that front, Stratton believes the GOP convention gave Democrats some help.

"Some of this regressive rhetoric about getting rid of Planned Parenthood or taking birth control out of a women's health plan - that is troublesome to voters," Stratton said. "Women are a larger majority of voters in Colorado than they are in a lot of states."

Both campaigns said having Denver as the site of last week's first presidential debate helped bring extra enthusiasm to their state organizations.

"It will be close here," Stratton said. "It will be close in Colorado regardless."