While I agree with most others here that CO is still more competitive than VA, it’s easy to forget just how ugly the trends are for Gardner/Republicans in this state, especially in the most populous counties that will actually decide the election:
County: 2014 results -- 2016 results -- 2018 results
Denver County: DEM +46 -- DEM +55 -- DEM +57
Boulder County: DEM +42 -- DEM +48 -- DEM +54
El Paso County: GOP +30 -- GOP +22 -- GOP +16
Weld County: GOP +27 -- GOP +23 -- GOP +21
Mesa County: GOP +41 -- GOP +36 -- GOP +26
Adams County: DEM +3 -- DEM +9 -- DEM +14
Arapahoe County: DEM +2 -- DEM +14 -- DEM +18
Jefferson County: DEM +<1 -- DEM +7 -- DEM +13
And when you consider that (1) Gardner only won by 2 in a GOP wave year, (2) population growth, generational turnover, and migration will likely make most of these counties (particularly Denver/the Denver suburbs, i.e. Adams, Arapahoe, Jefferson) even more Democratic-friendly in two years, (3) even then he will need to hold his own in the more rural/Hispanic Southern part of the state, (4) he will have to contend with increasing polarization and sharing the ballot with Trump, and (5) that he will likely face a much stronger opponent than Udall, yeah... the fat lady hasn’t sung yet, but she’s sure getting warmed up.
Clearly a Lean R race@Cook.