Former U.S. Attorney Matt Whitaker keeps the race the closest, running with 34 percent support to Braley's 43 percent support. That's due, in part, to the fact that Whitaker is the best known of all the Republican contenders, with 23 percent offering an opinion of the candidate.
Energy executive Mark Jacobs, talk radio host Sam Clovis, and State Sen. Joni Ernst all lag Braley by 12 points. And Braley leads David Young, the former chief of staff for Sen. Chuck Grassley (R-Iowa), by 13 points.
Each of the candidates is relatively unknown, however, with none above 25 percent in name recognition.
But Braley currently leads with independents and is seen favorably by a plurality of voters, while every Republican tested is seen unfavorably by more voters than favorably.
Republicans can take heart in President Obama's declining approval in the state.
He's now underwater, with 46 percent of those polled approving of the president, while half disapprove. That's down from February, when 49 percent approved and 47 percent expressed disapproval with Obama.
The survey was conducted among 668 registered voters from July 5-7, and has a margin of error of plus or minus 3.8 percentage points.
This post was updated at 4:05 p.m.