WASHINGTON, June 8 (UPI) -- The question of evolution has worked its way into the U.S. presidential campaign because three GOP candidates have said they don't believe in it.

Sen. Sam Brownback of Kansas, Rep. Tom Tancredo of Colorado and former Arkansas Gov. Mike Huckabee have been on the defensive ever since they indicated in a debate last month they don't believe in evolution, USA Today reported Friday.

Even though the three are not likely to win the GOP nomination, Democratic strategist Mark Mellman says they make their party look like "a front for the Flat Earth Society."

Mellman, who served as John Kerry's 2004 pollster, says the trio might cause serious damage with swing voters who are culturally progressive.

Brownback, Huckabee and Tancredo say their religious views are compatible with science.

Huckabee, a Baptist minister, argues voters are interested in things like gas prices, healthcare, college tuition and Iraq, not evolution.