DES MOINES-At the dawn of the midterm election season, when Republican dreams of winning control of the Senate still seemed distant, the open seat in Iowa was barely on the radar of the marquee races to watch.

But with only three months of campaigning to go, it's not an overstatement to say Democrats now worry that their ability to retain the Senate majority hinges to a large degree on the outcome of the race in Iowa.

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Rep. Bruce Braley, the Democratic nominee, has struggled to meet lofty expectations and is now locked in a tough contest with Joni Ernst, a Republican state senator.

"The pressure is to make sure Iowa voters understand the clear choice they have in this election between me and my opponent because of the huge impact it's going to have on their future," Braley told ABC News on Thursday at the Iowa State Fair.

He did not dismiss the suggestion he's the underdog in the race.

"I've always felt like when you're running in a race in a state like Iowa, you're the underdog because this is a very purple state," he said.