On election night, Democrats must carry large majorities in their three largest counties of Boulder, Denver and Pueblo. Similarly, Republicans need big votes in Douglas, El Paso, Mesa and Weld counties. The two swing counties of Arapahoe and Jefferson will likely decide the winner, which is why the candidates most frequently visited them, especially the last couple of weeks.
Also, Larimer County tends to lean Republican as Adams does Democrat. By how much in a close election will help determine the winner.