Is the "blue wave" turning purple?

Republican-affiliated voters have outpaced Democratic-affiliated voters in early voting in seven closely watched states, according to data provided by TargetSmart and independently analyzed by the NBC News Data Analytics Lab.

GOP-affiliated voters have surpassed Democratic-affiliated ones in early voting in Arizona, Florida, Georgia, Indiana, Montana, Tennessee and Texas, the data showed.

Only in Nevada have Democratic-affiliated voters exceeded Republican-affiliated voters so far in early voting, according to the data.

Key Senate races are underway in seven of those eight states and will prove pivotal in determining which party controls the chamber.

The latest data suggests robust enthusiasm among early Republican voters that could put a dent in Democratic hopes for a "blue wave" in next month's midterm elections.

Republicans typically dominate early voting by absentee ballots, while Democrats tend to have the advantage with in-person early voting. So, for example, the entire early voting picture in Florida, which has yet to begin in-person voting, is incomplete.

In Arizona — where two members of the House, Democrat Kyrsten Sinema and Republican Martha McSally, are in a neck-and-neck contest to fill retiring Republican Jeff Flake's Senate seat — 44 percent of early voters had a Republican affiliation, compared to 33 percent who had a Democratic affiliation. Twenty-three percent of early voters were not affiliated with either major party, and thus grouped as "other" in NBC News' partisan analysis.

In Florida — where Democratic Sen. Bill Nelson is running for re-election in a tight race against Republican Gov. Rick Scott — 44 percent of early voters had a Republican affiliation, versus 38 percent who had a Democratic affiliation and 18 percent who were not affiliated with either party.

In Indiana — where Democratic Sen. Joe Donnelly is facing a re-election challenge from Republican businessman Mike Braun — 51 percent of early voters had a Republican affiliation, compared with 39 percent who had a Democratic affiliation and 10 percent who were not affiliated with either party.

In Montana — where Democratic Sen. Jon Tester is up for re-election in a state that President Donald Trump won by 21 points — 46 percent of early voters had a Republican affiliation, compared with 29 percent who had a Democratic affiliation and 25 percent who were not affiliated with either party.

In Tennessee — where former Democratic Gov. Phil Bredesen is in a close race with Republican Rep. Marsha Blackburn to fill retiring Republican Bob Corker's Senate seat — 63 percent of early voters had a Republican affiliation, compared with 30 percent who had a Democratic affiliation and 7 percent who were not affiliated with either party.

In Texas — where Republican Sen. Ted Cruz is attempting to hold off Democratic Rep. Beto O'Rourke — 53 percent of early voters had a Republican affiliation, compared with 43 percent who had a Democratic affiliation and 4 percent who were not affiliated with either party.

People wait at a polling place in Houston on Monday, the first day of early voting in Texas. Loren Elliott / Getty Images

On Monday, the first day of early voting in Texas, thousands of people were camped out at an early voting location in Houston hours before it opened, The Houston Chronicle reported.

And in Georgia — where civil rights groups have sued Georgia Secretary of State Brian Kemp, the Republican candidate for governor, saying the method his office uses to verify new voter registrations is discriminatory — 52 percent of early voters had a Republican affiliation, versus 43 percent who had a Democratic affiliation and 5 percent who were not affiliated with either party.

On the other hand, in Nevada — where Republican Sen. Dean Heller is up for re-election in a close race against Democratic Rep. Jacky Rosen — 45 percent of early voters had a Democratic affiliation, compared with 38 percent who had a Republican affiliation and 18 percent who were not affiliated with either party.

The data provided by TargetSmart and analyzed by NBC News also revealed additional patterns in early voting.

Women voters have outpaced men voters so far in Florida (55 percent to 45 percent), Georgia (54 percent to 46 percent), Indiana (53 percent to 46 percent), Montana (49 percent to 48 percent), Tennessee (52 percent to 48 percent) and Texas (59 percent to 41 percent), the data showed.

Male voters have outpaced women voters so far in Nevada (49 percent to 47 percent), the data shows. In Arizona, 48 percent of men and 48 percent of women have voted so far.

Suburban voters have outpaced rural and urban voters in Florida (43 percent suburban, 34 percent urban, 22 percent rural), Georgia (57 percent suburban, 31 percent rural, 12 percent urban), Indiana (45 percent suburban, 39 percent rural, 16 percent urban), and Tennessee (56 percent suburban, 33 percent rural, 11 percent urban).

Meanwhile, rural voters have outpaced suburban and urban voters in Montana, and urban voters have outpaced rural and suburban voters in Arizona and Texas.

As of Oct. 22, over 5 million votes have been cast early or absentee in the 2018 midterm elections nationwide.

Data analysis conducted by the NBC News Data Analytics Lab. Voter file data, collected by TargetSmart, contains information on most voters’ turnout history and selected demographic information.