Washington (CNN) Republican Sen. Dan Coats won't run for re-election in 2016, ending his political comeback while creating an opening for one by his long-time Indiana rival -- former Democratic Sen. Evan Bayh.

The two have swapped the Senate seat since 1989. Coats first retired from it in 1998, dodging what would've been a high-profile challenge from Bayh. Then Bayh retired in 2010, ducking Coats, who'd called his comeback bid unfinished business.

Now, as Bayh considers a return of his own -- he's still got $10 million in his campaign bank account from 2010 -- Coats will retire again, he announced Tuesday.

Coats, 71, said in a statement that he has "concluded that the time has come to pass this demanding job to the next generation of leaders."

"Until the end of my Senate term, I pledge to my constituents that I will continue to focus all of my time and energy on the major challenges that Hoosiers sent me to Washington to address," Coats said in a statement.

Read More