NASHUA, N.H. - Libertarians and conservatives have banded together in a diverse coalition to try to end New Hampshire's reputation as a RINO preserve.

Calling itself the 603 Alliance after the state's area code, the group plans to stage a caucus in October to unify behind a single conservative candidate before the GOP presidential primary three months later. Organizers say they are sick of the nation's first primary anointing centrists they consider "Republicans in Name Only."

John McCain (twice) and Mitt Romney won the last three New Hampshire Republican primaries.

"We must not again fall to the quadrennial head fake," State Rep. Bill O'Brien, a former House speaker, told a crowd of about 150 activists from more than two dozen right-leaning organizations at a conference here April 19.

"It starts off with the establishment Republicans and the liberal media telling us we've got to nominate a moderate so we can win, and then that moderate loses because he cannot draw any significant distinction between himself and the Democrat," O'Brien said.

With fewer social conservatives and evangelicals than Iowa and South Carolina, which bracket the state with a caucus and a primary, respectively, New Hampshire has become a cushion against early losses for more establishment-favored GOP candidates.

In addition, unaffiliated voters can pick either party's primary; in 2012, these independents were 45 percent of the electorate in the GOP contest.

To fight back, the 603 Alliance plans to choose from a slate of candidates likely to include Wisconsin Gov. Scott Walker, Texas Sen. Ted Cruz, and Kentucky Sen. Rand Paul. Organizers say Florida Sen. Marco Rubio and Louisiana Gov. Bobby Jindal might get some support from the group, as might physician Ben Carson, former tech executive Carly Fiorina, and former Pennsylvania Sen. Rick Santorum.

Former Florida Gov. Jeb Bush or New Jersey's Gov. Christie, considered moderates by the activists, probably will not win the caucus - though organizers said they would be on the group's ballot if they are running.

The Iowa-style caucus is scheduled for Oct. 17 at a to-be-determined venue, open to registered New Hampshire Republicans and undeclared voters who voted a GOP ballot in 2012, though rules are still being finalized. Participants would agree to support the winner.

Voters would gather in groups supporting various candidates. After the first vote, the two smallest groups would dissolve, and backers of those contenders would have to join another group. The process repeats until one candidate remains.

Organizers hope to be able to influence up to 25,000 votes in next year's primary.

"It's going to be a tough thing getting everybody to fall in line with that strategy and support somebody who may not be their first choice, but we feel it's important to do something, otherwise we'll wind up with a fragmented field of conservative and constitutional candidates - and be shut out," Jim Kofalt of Wilton, founder of a tea party group and a 2014 candidate for the state House, said in an interview.

The alliance comprises a spectrum of right-leaning groups: tea party activists, libertarians, gun-rights advocates, and social conservatives. They share beliefs in free markets and limited government.

None of the leaders involved predicted outright victory in the primary, though they said that would be nice.

"The main idea is to try to give some momentum coming out of New Hampshire to one of these conservatives," Kofalt said. Beyond that, the aim is a "stronger voice for conservatives" in state politics.

"We're reaching out to the people who haven't been voting, who've been discouraged and disaffected," said Fran Wendelboe, a former state representative who heads the Conservative Business League of New Hampshire and who calls herself a social conservative.

Some strategists and activists believe there are multitudes of "drop-off" conservative voters, who cast ballots in 2004 for the reelection of President George W. Bush and then stayed home in 2008 when McCain was the nominee. Wendelboe said, for instance, that the group would look for such voters in New Hampshire's evangelical churches.

The backdrop to the effort is several years of tension between establishment leaders and grassroots conservatives in the state GOP.

One of its organizers, tea party activist Jack Kimball, was elected chairman of the New Hampshire GOP in 2011 before he was ousted in a coup led by top Republican elected officials in the state. Another, Andrew Hemingway, was a libertarian candidate for governor last year who lost the nomination to establishment pick Walt Havenstein, who went down to defeat in the general election.

O'Brien, who addressed the meeting, was elected state House speaker after the GOP took back the chamber in 2014, but another Republican representative seized the job from him with a coalition of moderates and the Democratic minority. O'Brien had been speaker in 2011-13.

When the 603 Alliance gathered, it was in the same Crowne Plaza Hotel ballroom where the New Hampshire GOP held its summit with 19 declared or potential presidential candidates, which had ended the night before.

Kimball roused the crowd, saying that "Agenda 21, regional planning, and NGOs" were "trying to control all of us - rack 'em, pack 'em, and stack 'em." Agenda 21 is a United Nations program for sustainable land use that many on the right believe will erode U.S. sovereignty and individual property rights.

He also slammed the Patriot Act, the National Security Administration's electronic eavesdropping, the militarization of local police departments, and the Environmental Protection Agency, "our own terrorist organization."

Speakers excoriated the Obama administration and Hillary Rodham Clinton, but the GOP, as well as Jeb Bush and Christie, received their share of abuse.

O'Brien ripped Bush for backing national Common Core education standards and favoring a path to citizenship for illegal immigrants - and for his "dynastic last name."

The activists said they were tired of being taken for granted by GOP leaders, expected to fall in line behind the latest moderate.

"We are the core, the real base, of the Republican Party," Hemingway said.

To him, the problem goes deeper than an intraparty dispute. "In America today, we have a ruling class, a combination of big government and big business," he said. "They have built a system that robs people of their freedom. . . . It's us vs. them."

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@tomfitzgerald