Tennessee state Rep. Joe Carr announced Wednesday that he was abandoning his challenge of Rep. Scott Desjarlais in next year’s Republican primary and instead launching primary challenge against Sen. Lamar Alexander.

Carr’s campaign manager, Chip Saltsman, didn’t see it coming.

“I was as shocked and surprised as you can imagine,” Saltsman told the Washington Examiner.

Saltsman, a longtime Alexander supporter, resigned from Carr’s campaign Tuesday with a scathing letter of resignation. “I signed up to help you run for Congress, not the Senate,” he wrote.

Carr had been performing respectably among the Republicans challenging the embattled Desjarlais in a primary, but he was lagging behind state Sen. Jim Tracy in fundraising.

When Carr told Saltsman about his plans Monday, he offered little explanation as to why he was ditching his congressional bid to run for higher office.

“He said, ‘This is the race I’m supposed to run,’ ” Saltsman said. “So I was like, ‘OK.’ ”

Saltsman said Carr had been approached prior to his congressional bid by state Tea Party activists who urged him to challenge Alexander.

Now that he has jumped into the Senate race, however, Carr will face difficult odds: Alexander’s favorability is steady at 53 percent, and he has built up a campaign war chest of roughly $3 million.