Former Gov. John Hickenlooper (D) has defeated incumbent Sen. Cory Gardner (R) in Colorado's Senate race, AP projects.Why it matters: It's the first Senate seat that Democrats have flipped this election as they seek to take control of the upper chamber.The big picture: In the lead up to the election, polls consistently showed Hickenlooper with a comfortable lead against Gardner. Cook Political Report rated the race as "leans Democratic."Hickenlooper, who served as governor from 2011 to 2019, ran for the Democratic Party's presidential nomination earlier this year, but he failed to gain major traction in the polls.Gardner was first elected in 2014 and had branded himself as a fierce ally of President Trump, including on controversial issues like the impeachment trial and Brett Kavanaugh's confirmation to the Supreme Court. Data: AP; Chart: Naema Ahmed, Andrew Witherspoon, Danielle Alberti/Axios