Eclipsed so far by better-financed rivals, the two are criticizing Mitt Romney's conservative credentials aggressively in the run-up to Saturday's Iowa straw poll.
Their hope is not so much to defeat Romney as it is to deny him an overwhelming victory. Both men calculate that a close second would damage the former Massachusetts governor and allow the runner-up to emerge as the favorite of social conservatives who will play an important role in the nominating campaign.
Only one, at most, can claim that mantle.
"This is a chance to break out," says Brownback, a 50-year-old Kansas senator who is an outspoken foe of abortion, embryonic stem-cell research and same-sex marriage. "We can finally start getting the national media."
Said Huckabee, a 51-year-old Southern Baptist minister and former Arkansas governor, "We want to do well to show that the momentum continues to build."
Although neither would concede that a poor showing would end their presidential hopes, others say it would be difficult to survive.
"I think there will be sort of a natural realignment after the straw poll," said veteran Republican strategist Bob Haus, who is not affiliated with any candidate. "One of them will emerge as a clear favorite and start to coalesce this constituency."
Ironically, Brownback and Huckabee have an opportunity because better-known rivals, Sen. John McCain, former New York Mayor Rudy Giuliani and former Sen. Fred Thompson, decided not to compete in the straw poll.
Their names will be on the ballot, but Romney has poured money into what his strategists hopes will be a triumph that confirms his standing as a top-tier contender.
The straw poll, expected to raise at least $1 million for the Iowa Republican Party, is expensive for candidates, who are charged a hefty fee for space at the event and usually cover the $35 per person cost for supporters to participate.
Up to 40,000 Republicans from throughout Iowa are expected to travel to the Iowa State University campus in Ames for the daylong event. The candidates will bus in many GOP voters, who will listen to speeches, dine on free meals and cast their ballot after showing Iowa identification and dipping their thumb into ink to ensure they only vote once.
Brownback conceded that he and Huckabee are seeking favor from the same conservative wing of the party.
"We do have a lot of the same appeal, there's no question about that," Brownback said. "We both do appeal to, as a base constituency, some of the same people."
Huckabee noted, "That's not the only constituency, but it's an important one and one we want to do well in."
Although Brownback said there's no special rivalry between the two, Iowa GOP executive director Chuck Laudner said it's clear the two are bracing for a collision.
"They're kind of going after the same coalition of folks," said Laudner, a main organizer of the straw poll. "I would expect they suspect there wouldn't be enough room for both of them."
Laudner stopped short, however, of predicting the loser of the competition would quickly leave the race.
Former Iowa Republican Chairman Richard Schwarm, who supports Romney, said the battle to winnow the field is inevitably intense.
"I think the race is between Governor Huckabee and Senator Brownback as to who can claim that constituency. At some point I don't see how it is big enough for both of them," Schwarm said.
Some dismiss the straw poll as nothing more than a beauty contest that rewards well-financed candidates who can pay to bring supporters to Ames. But the event has a history of predicting the outcome of the caucus — and forcing the end of campaigns.
In the 1999 straw poll, then-Texas Gov. George W. Bush won easily and cruised to a caucus win. Four GOP candidates — Lamar Alexander, Elizabeth Dole, Gary Bauer and former Vice President Dan Quayle — dropped out after poor showings in Ames.