Why Dems are more confident in Colorado's U.S. Senate race, in 1 chart

Compared to the 2014 election, Democrats are more confident in Colorado's U.S. Senate race this year because of a single data point: voter registration.

By the numbers: Republicans counted 24,000 more registered voters in Colorado than Democrats in November 2014, a roughly 1 percentage point advantage.

• Now, registered Democrats outnumber Republicans by 125,000 — a 3-point edge, an Axios Denver analysis finds.

Why it matters: Elections are won by those who show up, but larger registration numbers give political parties a cushion against a gap in enthusiasm or turnout.

Flashback: Republicans won big in 2014 in Colorado and upset an incumbent Democrat to send Cory Gardner to the U.S. Senate

BFD: Fewer than 1 in 4 Colorado voters are affiliated with the Republican Party — a stunning 6.6 percentage point decline in eight years.

• Democratic registration fell 3 points in the same period.

Of note: Unaffiliated voters are the largest voting bloc in Colorado, a number that's skyrocketed since the state made it the default affiliation when registering to vote.

• 46% of registered voters are unaffiliated, according to Sept. 1 numbers.