The University of Denver professor who has been seeking the Democratic nomination to challenge Republican U.S. Sen. Cory Gardner ended his campaign Monday.

David Goldfischer, who jumped in the crowded primary in December, said in a release that his efforts to petition onto the ballot fell short.

An associate professor at DU’s school of international studies, Goldfischer brought a national security perspective to the race but failed to make a splash in a field that includes former Colorado Gov. John Hickenlooper, former state House Speaker Andrew Romanoff and a number of progressive candidates.

“David entered the race to help confront the grave threat to our 243-year-old democracy posed by Donald Trump and his corrupted Republican Party,” his campaign said in a statement.

“Senator Cory Gardner knows full well that his acquittal vote helped unleash Trump to further sabotage our laws and institutions, and to cheat to win with Russian help,” Goldfischer’s campaign added, referring to the incumbent’s vote in the Senate impeachment trial.

Goldfischer didn’t make an endorsement in the primary, which now numbers eight candidates. Including Goldfischer, 12 Democrats have dropped out of the race since campaigning began in late 2018.