It's official: Aurora City Councilman Ryan Frazier is the first Republican to get serious about taking on U.S. Senator Michael Bennet, the Democratic political newbie recently appointed to replace Ken Salazar when the latter became the nation's new Interior Department secretary. The Hill is reporting that Frazier announced the launch of an exploratory committee yesterday during an anti-tax ("Tea Party") rally in Grand Junction. Although he's not the first choice of GOP leaders in the Washington beltway, Frazier recently defeated Weld County District Attorney Ken Buck, attorney Dan Caplis, and former Congressman Bob Beauprez in a straw poll in conservative Douglas County. Frazier, an African-American, "may be a dyed-in-the-wool fiscal conservative" but tends to be more liberal on social issues than the party's Christians, according to Westword, which notes, for instance, that he supports benefits for same-sex couples. The larger question is whether Bennet, the former Denver Public Schools chief, is vulnerable. Although some speculate that he may face a Dem primary challenge from former state House Speaker Andrew Romanoff, there's also evidence that Bennet is entrenching himself well, according to 5280.