"From the day I first entered this race we knew we could not win without a strong, grassroots campaign to carry us across the finish line," Capito said in the same emailed statement.
"The fact that thousands of West Virginians have donated both their money and time to this campaign is truly humbling."
Capito announced her candidacy in late 2012. In early January, Rockefeller said he would not seek re-election.
Long rumored to be interested in seeking the Democratic nomination, in September Secretary of State Natalie Tennant officially announced her candidacy. Tennant officially kicked off her campaign a few days before the fundraising deadline for the third quarter.
A Tennant spokeswoman said the campaign would be ready to discuss its fundraising totals next week. Federal candidates must file fundraising reports for the third quarter by Tuesday.
Political pundits said the GOP stood a good chance of winning the seat before Tennant entered the race.
Stu Rothenberg of the Rothenberg Political Report and Larry Sabato, a political analyst at the University of Virginia who writes 'Sabato's Crystal Ball,' both say Tennant's candidacy makes the race closer but still believe Republicans have the advantage.