The convergence of two developments has ignited the fears. The state Republican Party’s 36-year-old summer straw poll in Ames, which has played a role in winnowing the field of candidates, is in jeopardy because many presidential hopefuls have said they will not spend money on an event they think offers more risk than reward.

And cable television stations have said their criteria for entry to the first two Republican presidential debates this year will be based on standing in national polls — which for the hopefuls puts a premium on building national name recognition rather than spending time and money in the states that begin the nominating contest.

Ms. Ernst, talking to reporters, encouraged the contenders to compete in the Aug. 8 straw poll.

“I think it is important, because we have a lot of candidates that will come out and attend events like this, but we’re not getting a read on how those candidates are doing,” Ms. Ernst said, adding, “So we really want the grass-roots activists to come out and vote on who they want to see as their candidate, and that’s what the straw poll will accomplish.”