The first is pragmatic: You live in a region where your party has long been thrashing in the wilderness, but you still want a say in choosing candidates. So you choke back tears while checking the other party's box on a voter registration form, cheered only by the prospect that the small mark will allow your voice to be heard.
The second reason could be called prophylactic, and it is widely viewed with disfavor except by certain right-wing radio personalities. In this scenario, you like (or at least tolerate) the candidate your own party is nominating, but change your registration so you can vote against his or her strongest opponent.
Rush Limbaugh called it "Operation Chaos" as he encouraged Republicans to cross party lines and vote for Sen. Hillary Clinton in Democratic primaries, a move he believed would prolong the nomination battle and weaken Sen. Barack Obama.
Jay Fawcett, the Democrat who lost the 2006 local congressional race to U.S. Rep Doug Lamborn, uses the word "Machiavellian" to describe Limbaugh's tactic. Though Fawcett admits there are valid reasons to switch parties, "I don't do it," he says.
Without data tracking changes in party affiliation (and tests to evaluate motivations), it's tricky to say if strategic realignments are common.
But the Aug. 12 primary election will tempt some voters in the Pikes Peak region to shift sides, if only for a few weeks. Depending on where you live, you could have up to three contested Republican races. County Democrats have nearly a full slate of candidates but nary a contested race.
Diane Kelly speaks openly about her reasons for becoming a Republican last month: It was the only way she could carry a petition to put Dan May on the primary ballot for district attorney. She also plans to vote for him in August.
Though she describes herself as a "pretty staunch Democrat," she backs May in his rematch of the 2004 primary against incumbent John Newsome. With no Democratic candidate, the Aug. 12 vote will determine who leads El Paso and Teller county prosecutors for the next four years.
"I would never have a say if I didn't switch parties," Kelly says.
May petitioned onto the primary ballot after Newsome was shown on a television news report drinking about a gallon of beer and then driving his county-owned vehicle.
Kelly says she made the same switch in 2004 because she preferred May's positions. Her support for May grew after her husband was killed in a 2006 crash with a drunken driver. She says she was disappointed by the lack of support and communication from Newsome's office.
Also on Aug. 12, Republicans in El Paso, Teller, Chaffee, Fremont and Lake counties, and part of Park County, will select Rep. Lamborn, Jeff Crank or Bentley Rayburn as the party's candidate for Congress. The winner will face Democrat Hal Bidlack in November.
Another hot GOP race matches Rep. Douglas Bruce and Mark Waller in State House District 15, including portions of eastern Colorado Springs and the county.
Bruce, formerly a county commissioner, was appointed last fall to the Legislature. Since taking office in January he has been a magnet for controversy, alienating him from local Republican leaders, many now supporting Waller. The winner will face Democrat Michelle Maksimowicz in November.
Timeline: The registration deadline for the Aug. 12 primary is Monday, July 14, also the deadline for changing party affiliation. Only registered Republicans or Democrats can vote in each party's primary, but unaffiliated registered voters (including self-described Independents) can declare a party at the polls.