Kenneth Robert Buck (born February 16, 1959) is an American lawyer and politician who has represented Colorado's 4th congressional district in the United States House of Representatives since 2015. From March 30, 2019, to March 27, 2021, Buck served as chair of the Colorado Republican Party, having replaced Jeff Hays. Formerly the District Attorney for Weld County, Colorado, Buck ran unsuccessfully for U.S. Senate in 2010, narrowly losing to Democrat Michael Bennet. In Congress, Buck has emerged as one of the foremost proponents of antitrust enforcement in the Republican Party. A staunch conservative as a member of the House Freedom Caucus, Buck was one of only four Republican votes opposing House Speaker Kevin McCarthy's April 2023 debt ceiling/deficit reduction bill, explaining in a subsequent Washington Times op-ed that "[i]f this plan with modest spending reductions is the best the GOP can provide, Americans could be forgiven for wondering what the point of a Republican majority in the House is."Buck announced in November 2023 that he would not seek a sixth House term, stating that his party's "insidious narratives breed widespread cynicism and erode Americans' confidence in the rule of law."