Whitaker announced Monday he plans to file paperwork with the Federal Election Commission to officially become a candidate later this week. The seat became competitive after Sen. Tom HarkinTom HarkinGrassley challenger no stranger to defying odds Clinton ally stands between Sanders and chairmanship dream Do candidates care about our health or just how much it costs? MORE's (D) decision not to seek reelection in 2014. 

Whitaker, a former University of Iowa football player, said he'd seek to emulate Sens. Rand PaulRand PaulPaul: Pence should oversee Senate ObamaCare repeal votes Healthcare fight pits Trump against Club for Growth GOP rep: Trump could be 'one-term president' if healthcare bill passes MORE (R-Ky.) and Ted CruzTed CruzPaul: Pence should oversee Senate ObamaCare repeal votes Senators introduce new Iran sanctions With no emerging leaders, no clear message, Democrats flounder MORE (R-Texas) if elected, and could draw some strong support from Tea Party and libertarian voters in the primary. But those views could be tough to sell statewide in the swing state.

Other potential GOP candidates include Secretary of State Matt Schultz (R), Iowa state Sen. Joni Ernst (R) and Sen. Chuck GrassleyChuck GrassleyFriends, foes spar in fight on Trump’s Supreme Court nominee Live coverage: Day three of Supreme Court nominee hearing Live coverage: Day two of Supreme Court nominee hearing MORE's (R-Iowa) chief of staff, David Young. 

GOP insiders expect both Schultz and Ernst to run. Young has been holding private meetings around the state, but it’s unclear whether or not he’ll run.

But that list is a decided letdown after some other Republicans took a pass on the race. 

Iowa Gov. Terry Branstad (R), Reps. Tom Latham (R-Iowa) and Steve King (R-Iowa) and Iowa Lt. Gov. Kim Reynolds (R) — all better-known candidates — have said they won’t run, as has Iowa Agriculture Secretary Bill Northey (R).

A number of Republicans privately told The Hill that they were concerned all the potential candidates would struggle to beat Rep. Bruce BraleyBruce BraleyTen years later, House Dems reunite and look forward Trump: Ernst wanted 'more seasoning' before entertaining VP offer Criminal sentencing bill tests McConnell-Grassley relationship MORE, who is expected to be the Democratic nominee.   

At this point, the party's best hope is that one of the candidate emerges a star following a hard-fought primary.

“I think a primary is probably the best thing, to have a candidate prove they have the chops and be able to raise money and run a strong campaign,” said David Kochel, a top adviser on Mitt Romney’s Iowa presidential campaigns in 2008 and 2012. Kochel has been busy connecting potential Senate candidates with the National Republican Senatorial Committee.

“You've got to put together a winning message, a strong coalition and raise enough money to run a strong statewide campaign,” he said. “Whoever does that could be a strong candidate against Braley, who's not that well-known outside of his district.”

Whitaker and Schultz are both very conservative, and have shown no signs they want to move to the middle as they look ahead toward a potentially bruising primary. 

Whitaker’s name-checking of Paul and Cruz, two hard-line conservatives, in his Monday radio interview indicates he’s looking to woo the state’s libertarian activists in the race. 

Schultz, who was the highest-ranking GOP official in the state to endorse former Sen. Rick Santorum’s (R-Pa.) presidential campaign, has close ties to the state’s highly active religious conservative movement.

Some Republicans are bullish about Ernst, a female military veteran who has a strong profile. But Ernst only recently won her state Senate seat and is unproven as a major candidate.

“Ernst is the least known of them all ... I know who she is and have seen her around but have never talked to her,” said Robinson, the former political director. “Whitaker and Schutlz and everyone else who's flirted with running I know very well. She's a candidate on paper. I'd reject the notion that she's the strongest in the general election.”