CHARLESTON, S.C. — With the Iowa caucuses less than three weeks away, top Republicans are expressing growing anxiety about the state of the party's raucous presidential primary — and what it could mean for its prospects of winning back the White House in 2016.

As they gathered here for the Republican National Committee's annual winter meeting, party officials voiced concern about everything from the possibility of a contested convention to whether changes they instituted to the debate schedule and primary calendar were having unintended consequences.

On nearly everyone's mind were Donald Trump and Ted Cruz, the insurgent front-runners who, many GOP officials are convinced, would imperil the party's 2016 chances.

"While I probably agree on lots of issues with Ted Cruz, I find his tone negative and divisive, and I think it would make it harder to win a general election," said Henry Barbour, an influential Mississippi committeeman and the nephew of former RNC hairman Haley Barbour. "Trump — look, I don't think he'd make our strongest general election candidate."

Many acknowledged that they've been blindsided by the unpredictable and turbulent nature of the race. Few foresaw such an unwieldy and rambunctious primary field — and no one guessed that, with just days before the first votes are cast, it would be led by Trump.

"We're all very surprised," said Jonathan Barnett, an Arkansas committeeman who has attended nine Republican national conventions. "We never thought there would be 17 candidates. And then Trump changed everything. No one saw that one coming. They didn't think he would go so far as he did or that he would pick up as much support as he did."

With so much uncertainty about the race, some acknowledged that they had begun to consider the impossible: a contested convention in Cleveland this summer. While the party hasn't had a contested convention since 1976 — when an insurgent Ronald Reagan was outmaneuvered and outmuscled by Gerald Ford — the sheer size of the primary field has many Republicans fearing that no candidate will win the majority of delegates needed to secure the nomination.