The 88-year-old Senator made his announcement on Twitter Friday morning at 4 AM before his morning run.
During a stop in the Quad Cities, he was asked whether he's been in office too long. Grassley says after 40 years, he'll leave it up to Iowans to decide.
"Every six years they've had a chance to vote me out of office. They approve of what I've done--that's why I'm re-elected."
The announcement comes after several other Republican senators up for re-election next year have announced plans to retire, including Senators Roy Blunt of Missouri, Richard Burr of North Carolina, Rob Portman of Ohio, Richard Shelby of Alabama, and Pat Toomey of Pennsylvania.
Three Iowa Democrats so far have announced plans to run for the Senate next year, including Abby Finkenauer, Glenn Hurst, and Dave Muhlbauer.
One Republican is also running, State Senator Jim Carlin.
