Long-time Iowa Sen. Grassley wins GOP primary

The longtime senator defeated one challenger in the primary
Iowa Sen. Chuck Grassley on Capitol Hill. Washington, D.C. (Undated)

Iowa Republican Sen. Chuck Grassley on Tuesday defeated Republican state Sen. Jim Carlin in the GOP primary.

The Democratic U.S. Senate primary race in Iowa between frontrunners Abby Finkenauer, a former congresswoman from Cedar Rapids, and retired Navy Adm. Mike Franken is among the state's most closely-watched races.

The winner will face the 88-year-old Grassley in November. He's held the Senate seat since 1981.