It might not be enough to blunt the momentum swinging nationally to Joe Biden and Bernie Sanders. But for Elizabeth Warren, Pete Buttigieg and Amy Klobuchar, high turnout in the Iowa caucuses may be their only chance.

One week from today in Iowa, Warren and Buttigieg will flex their organizational advantages for the first time, and Klobuchar will test the extent of her appeal to rural Democrats. Their prospects are pinned to uncertain turnout models in which Sanders does not dramatically expand his base — and Biden does not consolidate moderate support.

“The national conversation seems to be moving past Pete, past Elizabeth, to Bernie and Biden. That’s where I think everything’s heading, or returning,” said Doug Herman, who was a lead mail strategist for Barack Obama’s 2008 and 2012 campaigns. “It’s kind of a reset back to the beginning of the race.”

But if there is high turnout in Iowa, he said, “It may help the other candidates: It may be what they need to stay viable.”