Donald Trump and Chris Christie are both outsized personalities, but only one of them is apparently big enough to speak at the CPAC conservative gathering next week – and it is not the New Jersey governor.

Just days after creating headlines by not inviting Christie to one of the biggest events on the Republican calendar, the American Conservative Union has again dismayed much of its core constituency by extending a hand to Trump, a reality TV star known for embracing the "birther" conspiracy theory that suggests Barack Obama may have been born outside the US.

"Donald Trump is an American patriot with a massive following among small-government conservatives. I look forward to welcoming him back to the CPAC stage next week," said ACU chair Al Cardenas.

Compare that to Cardenas' explanation of why he had snubbed Christie: "CPAC is like the all-star game for professional athletes; you get invited when you have had an outstanding year. Hopefully he will have another all-star year in the future, at which time we will be happy to extend an invitation. This is a conservative conference, not a Republican party event."

The Conservative Political Action Conference, which is hosted by the ACU, is the main gathering for rightwing Americans inside and outside the Republican party. It is hugely influential for anyone seeking to woo American conservatives, and its approval is often seen as a key stepping point on any Republican politician's ambitions to mount a campaign for the presidency.

However, since Mitt Romney was beaten in last year's presidential election, the Republican party has embarked on a broad civil war that has pitted an unrepentant conservative rightwing against modernisers seeking to expand the party's appeal to minorities and more centrist voters.

Christie has been identified with that more moderate wing, and is also fighting conservative ire after publicly praising Obama's handling of superstorm Sandy, which hit New Jersey just before the election and devastated wide areas of the state. Cardenas has publicly stated that Christie had not acted like a true conservative recently when it came to trying to cut spending, citing his acceptance of government help for Sandy and his proposal to expand Medicaid.

By contrast, Cardenas has had nothing but warm words for Trump on Tuesday. "Mr Trump's previous CPAC appearance was hugely popular among our attendees, and we expect it will be even more popular this year," he said in a statement.

That performance was a barnstormer, in which Trump earned repeated and enthusiastic applause for his die-hard brand of conservatism and showmanship. It included such blunt talk on foreign policy as this statement on the threat of Somali piracy: "Give me one admiral – one good admiral – and a couple of good ships, and we'd blast the Somalia pirates out of the water so fast."

He also proposed replacing the Environmental Protection Agency with an Environmental Solutions Agency and said that too many countries that the US traded with were "screwing us".

But those comments were nothing compared to some of the gaffes and stunts that the man known most often as "The Donald" has previously made, especially while teasing the media with the idea that he might run for the White House.

In trying to support another rightwing conspiracy theory, Trump has famously offered $5m for copies of Obama's college transcripts and passport application. During 2011, when speculation over a Trump run for the White House was at its height, Trump was held up by some observers as an example of just how extreme the Republican party had become. His dogged belief in birtherism saw more than 400,000 people sign a petition to have Macy's sever its business relationship with him.

Not surprisingly, some conservative figures expressed disappointment over the invitation to Trump, especially in the light of Christie's rejection. "Oh, brother. CPAC has now jumped the shark by inviting the pro-choice billionaire buffoon Donald Trump," wrote Washington Post conservative columnist Jennifer Rubin.

On Twitter, numerous conservatives expressed disappointment. "Is CPAC trying to sabotage the conservative movement?" wrote conservative blogger Sonny Farmer. "CPAC is dead," said influential rightwing blogger Michelle Malkin. © Guardian News and Media 2013