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Jeff Johnson replaced his campaign manager Friday, as his challenge to Gov. Mark Dayton intensifies and Election Day gets closer.

Johnson dropped the surprise news in an afternoon press release. David Gaither, a former state senator and chief of staff to former Gov. Tim Pawlenty, is taking over the campaign. He's replacing Scot Crockett, who led Johnson's successful effort to claim the Republican Party endorsement in May and to win the GOP gubernatorial primary in August.

"David Gaither's skills and experience will be invaluable to my campaign as we make the final push to victory in the next six weeks," Johnson said. The campaign said Crockett would return to his home in Virginia to be with his family, but would continue to advise the campaign.

With the election near -- absentee balloting started Friday -- Johnson has struggled with an under-funded campaign and low name recognition. A Star Tribune poll of 800 likely voters taken in early September found that a third of respondents had never heard of Johnson, and another 40 percent had not formed an opinion of him.

The same poll had Dayton leading Johnson, 45 percent to 33 percent.

Johnson's campaign has also yet to air television commercials, while the DFL and third-party group Alliance for a Better Minnesota have already aired ads critical of him. Johnson said earlier Friday he would have a TV ad on the air by the end of September.

Gaither, who like Johnson hails from Plymouth, served as a Republican state senator from 2002 to 2005. He resigned to serve as chief of staff under Pawlenty, generally considered the top staff position in any administration. Gaither stayed in the job only a little over a year.

Most recently, Gaither sought a return to elected office when he ran for his old Senate seat in 2012. He lost to Sen. Terri Bonoff, DFL-Minnetonka. The Johnson campaign said Gaither would take a leave of absence from his job as executive director of the Minneapolis-based International Education Center.