More Republicans than Democrats have cast ballots since early voting got under way Monday in Colorado, a state with one of this cycle's tightest Senate contests. 

Numbers released late Wednesday from the Colorado secretary of state's office revealed that 81,545 Republicans have cast an early ballot, compared to 71,325 Democrats. More than 41,000 unaffiliated voters have already weighed in, according to the data. 

So far, Republican early voters outweigh Democrats in all but two of the state's counties: Boulder and Denver. 

It's much the same story in Nevada, where the early vote totals are likely already worrying Democrats. According to data compiled by George Mason University's Michael McDonald, Democrats are underperforming with early voters in crucial Democratic terrain.

In Clarke County, which houses Las Vegas, 46 percent of those who have already voted early are Democrats, compared to 38 percent who are Republicans. In the 2008 election, McDonald's totals show that Democrats made up 52 percent of the early vote in the county, to just 30 percent of early votes cast by Republicans. 

The early vote will be a key indicator for Senate Majority Leader Harry ReidHarry ReidDraft House bill ignites new Yucca Mountain fight Week ahead: House to revive Yucca Mountain fight Warren builds her brand with 2020 down the road MORE (D-Nev.), whose race against Republican Sharron Angle could hinge on the effectiveness of the Democrat's turnout operation.     

Early voting will also be telling for Sen. Michael BennetMichael BennetTrump's FDA nominee clears key Senate committee Dems knock Trump on Earth Day Dem pushed plan for both sides to admit to abusing Senate rules: report MORE (D-Colo.), who is fending off a challenge from Republican Ken Buck. Bennet's campaign brought in former President Bill ClintonBill ClintonBuzzFeed toasts free press at alternative WHCA party Why Trump sitting out the correspondents' dinner is a huuuge mistake Larry Summers: Mnuchin squandering his credibility with Trump tax proposal MORE for a rally this past Monday to mark the start of early voting in the state.  

Both campaigns are pouring resources into early voting, which elections officials in Colorado anticipate could account for more than a quarter of all votes cast in November's midterm elections. 

In the terrain that makes up Colorado's 4th congressional district, where Rep. Betsy Markey (D) faces a tough challenge from Republican Cory GardnerCory GardnerOvernight Defense: Commander calls North Korea crisis 'worst' he's seen | Trump signs VA order | Dems push Trump to fill national security posts Senators get North Korea briefing in unusual WH visit A Vandenberg movement in Congress MORE, the GOP holds a slight edge in the number of early votes, too. 

Markey is trailing Gardner by just three points, according to numbers from The Hill Midterm Election Poll. The Republican leads 44 percent to 41, with 14 percent of likely voters undecided. 

It's a bit of a different story in North Carolina, though. McDonald's breakdown of the early vote numbers there shows Democrats actually outpacing Republicans, 44 percent to 38. Another 17 percent of voters who have already cast ballots are unaffiliated. 

In that state, some Democrats have been trying to make the case that Sen. Richard BurrRichard BurrTrump voter who cast ballot illegally won’t be charged Burr: US in new Cold War with Russia Senator: No signs of GOP 'slow-walking' Russia investigation MORE (R-N.C.) is vulnerable this year. He faces Democrat Elaine Marshall, who has crept a bit closer to the incumbent in polls, but still trails. 

The latest numbers from Public Policy had Marshall within eight points of Burr, but that is the only public poll of late to show Burr with anything less than a double-digit lead.