WASHINGTON (CNN) - Former Sen. Dan Coats, R-Indiana, is expected to announce Wednesday that he will challenge Sen. Evan Bayh, D-Indiana, in November, a Republican source told CNN.
Coats held the Senate seat that Bayh now occupies from 1989 to 1999.
It is a big recruiting success for Senate Republicans, who hope that voter frustration with President Barack Obama's handling of health care and the economy will translate into electoral wins in the mid-term elections.
Republican Scott Brown's surprising victory in last month's Massachusetts special election has given the GOP hope of evening the odds in the Senate. Democrats control the chamber, 60-40, with the support of two independents. When Brown is sworn in next week, Democrats will hold the chamber by one less vote, effectively ending their supermajority in the chamber.
Coats was appointed to the Senate seat after Sen. Dan Quayle was elected vice president in 1988. Coats went on to win a special election to serve the rest of Quayle's unexpired term, as well as his own full six-year term. Coats chose to retire instead of run for re-election. Bayh won the seat in November 1998 and is seeking a third term.
The GOP source spoke on the condition of anonymity.
The former senator was ambassador to Germany from August 2001 to February 2005 in President George W. Bush's administration.
Before joining the Senate, Coats served in the House from 1981 to 1988. He is currently a senior policy adviser at King & Spalding.
"Howey Politics Indiana" first reported Coats' candidacy late Tuesday.