Rep. Mick Mulvaney (R-S.C.) said Rick Perry’s flat-tax plan, which he announced Tuesday in South Carolina, will reinvigorate the Texas governor’s struggling campaign.

“It’s the first time since the first California debate that I felt a lot of energy behind Gov. Perry’s campaign,” Mulvaney said Thursday on MSNBC.

Perry shot to the top of the polls after announcing his candidacy in August, but is now sitting at no better than fourth place in any of the key early-voting states, according to the latest CNN-Time-ORC polls.

“I was very excited to see him go with the flat tax,” Mulvaney said. “It’s very similar to what we’ve been talking about in terms of the Republican Study Committee, the conservative group within the House Republicans, and he went a little bit further than I think we’re going to go even. I was enthusiastic about somebody actually taking some bold steps.”

The Perry plan would create an alternative 20 percent flat tax, a privatized option for Social Security and a hike in the eligibility age for Social Security and Medicare. Taxpayers would have a choice between keeping their current tax rates or taking the 20 percent flat tax, while all standard deductions and tax credits would be preserved.

“I look specifically back home, to South Carolina, which is a fairly conservative state and an early primary state,” Mulvaney said. “Some really big names in South Carolina politics from the Tea Party all the way over to the establishment are sort of rallying to Mr. Perry now that he’s offered real ideas.”

On Tuesday, Perry landed the endorsement of South Carolina state House Speaker Robert Harrell (R). He also met with Gov. Nikki Haley (R), although she isn’t expected to give her coveted endorsement until early next year.

Republican candidates have been looking for a way to make inroads on Herman Cain’s success. Cain surged to the head of the polls after his 9-9-9 tax proposal gained publicity.

“One of the reasons you see Herman Cain do so well is that he’s been one of the few folks up until this week to offer specific ideas,” Mulvaney said. “And now that Gov. Perry has matched that, I think you’ll see his campaign start to pick up some energy as well.”

Opponents of the flat tax have slammed it as regressive, and said it will add to the deficit by lowering taxes without opening any additional revenue streams.