"Over the next month, Club for Growth will educate Georgia voters about Doug Collins’ record on economic issues and demand that he change his ways," David McIntosh, the Club's president, said in a statement.

The advertising blitz comes after the Club publicly chastised Collins for having a 57 percent score on their legislative scorecard last year, though he has an 80 percent lifetime score with the Club.

Along with the Club, the National Republican Senatorial Committee and several top allies to Republican leadership, including a super PAC aligned with Senate Majority Leader Mitch McConnell, rallied around Loeffler and panned Collins' run as a selfish move that was harmful to the party.

Collins pushed back against the NRSC response on Twitter and brushed off any concerns about creating an intraparty rift when he announced his bid in an interview on "Fox and Friends" Wednesday morning.

"I think we fought for the president, we fought for our state and we fought for this country," Collins said. "And we're going to continue to do that. I look forward to a good exchange of ideas and look forward to this election."

While Loeffler has significant support from Senate Republicans, Collins' campaign has some clear signs of strength. An internal poll conducted in December showed him leading Loeffler by 21 percentage points in the all-party race in November, holding a significant edge among Republican voters. He also had a positive image among all voters statewide — and an overwhelmingly positive image among Trump supporters, according to the poll.

Loeffler's campaign has since spent or booked $2.6 million on TV in Georgia to boost her image.

Collins has also received support from some state legislators and some prominent conservatives, including radio host Mark Levin and lobbyist Matt Schlapp, who is close to the administration, both of whom tweeted support for Collins after his announcement.

Alex Isenstadt contributed to this report.