From this article
"With just two weeks until the election, Republicans are seeing a surge in voter registration in the battleground states of Arizona, North Carolina, Pennsylvania and Florida. Republicans have out-registered Democrats in those states by about 445,000 to 224,000 since the primaries, with an aggressive push since August. It marks the first time since 2004 that more Republicans than Democrats have registered to vote in the final months of an election.
Republicans have never had a registration advantage over Democrats in Florida. This year they have narrowed their lead, leaving Democrats with 136,000 more registered voters, nearly half of what they had in 2016 and the smallest gap that has existed between the parties in more than 40 years.
In three months, Republicans registered 30,000 more Arizona voters than Democrats, a state that already has a 97,000-person GOP advantage. In North Carolina, Republicans signed up 28,774 more voters than Democrats, eating into their partisan advantage by more than half. In Pennsylvania, which Trump won in 2016 by 44,000 votes, Republicans eroded the Democratic advantage by 24%. In the last three months, Republicans registered 71,922 more Pennsylvania voters than Democrats.
In Florida, Colorado, Maine, North Carolina and Pennsylvania, Democrats made up a smaller share of new registrants during this election cycle, according to a study by the Democratic data firm TargetSmart...."