With rumors circulating about Voinovich's possible retirement, former Director of the Office of Management and Budget, United States Trade Representative, and Congressman Rob Portman and State Auditor Mary Taylor were considered the main contenders for the Republican nomination.

[3] Former Ohio Secretary of State Ken Blackwell was also considered a potential candidate, but declined in order to run for chairman of the Republican National Committee.

[5] Thomas Ganley, a Cleveland car dealer, launched his campaign for the nomination in April, after Portman had collected support from most of the Ohio Republican establishment.

[9] Congressman Tim Ryan, Secretary of State Jennifer Brunner, and Lieutenant Governor Lee Fisher were considered leading contenders to run against George Voinovich.

[12] Cuyahoga County Commissioner Peter Lawson Jones and Ohio State Representative Tyrone Yates considered running, but both withdrew from consideration.

[19] Charlene Renee Bradley and Traci Johnson also filed to run in the Democratic primary.

[34] Originally, the election was seen as a toss-up, as Portman's experience in the Bush administration was considered a liability for him.