With a little more than 100 days to go before Election Day, the presidential campaigns for Republican John McCain and Democrat Barack Obama are beginning to build their Colorado organizations.

Obama's campaign has announced it will open four campaign field offices on Tuesday in Boulder, Colorado Springs, Denver, and Pueblo - with more on the way, said spokesperson Matt Chandler.

The Illinois senator's campaign already has more than 50 staffers in the state, according to Chandler (who himself arrived in Denver only about two weeks ago).

McCain's campaign has been building their organization, too - the Arizona senator's state campaign headquarters is already open in Centennial, and five coordinated campaign field offices are located throughout the state.

The McCain campaign currently has six full-time staffers in the state, though that number will soon grow, said spokesperson Tom Kise (who started as McCain's south central regional communications director earlier this month).

Unlike during previous presidential elections, Obama's campaign is not joining the state's Democratic coordinated campaign -- a decision that some state Democrats have warned will cause redundancy and waste resources, despite state party reassurances.

The decision not to join the coordinated campaign may stem in part from a feeling that Obama can build on the significant primary organization he established in Colorado in advance of the Feb. 5 Democratic caucuses. At the end of January, Obama opened 12 field offices in Colorado and had a staff of 30 - and, perhaps most significantly, formed a widespread grassroots network that helped him defeat caucus opponent Hillary Clinton in Colorado by a 2-to-1 margin.

"That network of volunteers, as well as actual infrastructure, is something we're certainly starting to tap back into," Chandler said.

McCain's caucus organization was significantly smaller, as Colorado Republican caucusgoers overwhelmingly picked former Massachusetts Gov. Mitt Romney.

But Kise said McCain's primary infrastructure in the state "was nothing to shake a stick at.

"We're going to have the resources to get things done on Election Day -- to make sure our message is out there," Kise said.

But while caucus organizations are geared towards turning out the party base, it's the state's large independent voting bloc that will likely play a pivotal role in determining who wins Colorado's nine electoral votes.

April 2008 party voter registration numbers from the Colorado Secretary of State - the latest available - show Colorado has 1,017,738  registered Republicans, 1,013,5487 registered independents, and 900,8231 registered Democrats.