The Iowa Republican says Young has quit his job, has hired consultants and is in the process of buying a house outside of Des Moines. Many of those consultants have ties to Grassley, including famed GOP ad maker Fred Davis, who's best known for Christine O'Donnell's "I'm Not a Witch" ad but who's had a string of successes, including Rep. Steve King's (R-Iowa) 2012 reelection campaign.

Young will join former U.S. Attorney Matt Whitaker (R) in the race. Other potential GOP candidates include Secretary of State Matt Schultz (R) and Iowa state Sen. Joni Ernst (R). A number of higher-profile Republicans have taken a pass on the race, leaving local strategists nervous about the strength of the GOP field.

On the Democratic side, Rep. Bruce BraleyBruce BraleyTrump: Ernst wanted 'more seasoning' before entertaining VP offer Criminal sentencing bill tests McConnell-Grassley relationship Trump's VP list shrinks MORE (D-Iowa) is the likely nominee to replace retiring 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 (D-Iowa).