Mike Johnston or Joe Salazar(D-CO) for US Senate in 2020.

[nkpolitics1212]

Johnston-D and Salazar-D are rising star former/Outgoing CO Democratic state legislators who ran for Statewide Office this year and lost in the primary. Based on process of elimination- both of these men are likely Democratic challengers against Gardner-R.
Hickenlooper-D is focused on the 2020 US Presidential Race.
Perlmutter-D is likely to remain in the US House until he leaves- ie DeGette-D
Kennedy-D and Markey-D have lost 2 elections in a row.
Neguse-D and Crow-D will seek re-election to the US House in 2020, then run for the US Senate in 2022/2028 when Bennet-D decides to retire or 2026 CO Governor when Polis-D is term limited from seeking re-election to a 3rd term.