Adams voted D +17 in 2012, D +9 in 2016, then D +16 in 2020.
Why did Adams have a right-trend from 2012 to 2016 before snapping back to Biden? It seems like the other Denver suburban counties (Jefferson, Arapahoe) were all trending left.
From Wikipedia
…In 2008, Colorado realigned to the Democrats, for U.S. President, with Democratic presidential pickup winner Barack Obama and his pickup of the state. (That year, and in 2012, Colorado was the Democrats’s No. 23 best-performed state. It was the Tipping-Point State in both 2008 and 2012. In 2016 and 2020, Colorado was the Democrats’s Nos. 16 and 14 best state.)
Since 2008, the number of votes cast for U.S. President, from Adams County (county seat is Brighton; most-populous city is Thornton), has increased by about 50 percent by Election 2020. This may explain some of these percentage-points margins.
Looking at theses percentage-points margins, in both 2016 and 2020, and that it performed within five percentage points from statewide outcomes, it may be wise to look to the outcome in 2024. It may be that Adams County is becoming a bellwether county-to-the-state in Colorado.