senator in 2014 by narrowly defeating the then-incumbent Democrat Mark Udall in a very successful year for the Republicans overall. Despite this, he is widely considered to be perhaps the most vulnerable Republican Senator up for re-election this cycle, due to Colorado's heavily Democratic trend in recent cycles and how frequently he has voted with Trump. The seat is expected to be highly competitive and is one of the top races both parties have their eyes on.

Republican primary

Candidates

Declared
 Cory Gardner, incumbent U.S. Senator

Endorsements

Results

Democratic primary

Candidates

Declared
Diana Bray, psychologist and climate activist
Lorena Garcia, community organizer
David Goldfischer, associate professor at the Korbel School for Int'l Studies at the University of Denver and national security advisor to the Dept of Defense, Dept of Homeland Security and U.S. Northern Command
John Hickenlooper, former Governor ofColorado State University professor and former chair of the Boulder County Democratic Party
Mike Johnston, former state senator and candidate for Governor of Colorado in 2018
Danielle Kombo, medical recruiter and businesswoman (endorsed Stephany Rose Spaulding)
Dustin Leitzel, pharmacist
Alice Madden, former majority leader of the Colorado House of Representatives
Keith Pottratz, technician and veteran (endorsed Lorena Garcia)
John F. Walsh, former U.S. Attorney for the District of Colorado (endorsed John Hickenlooper)
Angela Williams, state senator (running for re-election)

Declined
Diana DeGette, incumbent U.S. Representative (running for re-election)
Kerry Donovan, state senator (endorsed John Hickenlooper)
Crisanta Duran, former speaker of the Colorado House of Representatives (ran for Colorado's 1st congressional district, then withdrew)
Jena Griswold, Colorado Secretary of State
Joe Neguse, incumbent U.S. Representative for Colorado's 2nd congressional district (running for re-election)
Ed Perlmutter, incumbent U.S. Representative for Colorado's 7th congressional district