Six-term Republican Sen. Dick Lugar of Indiana is facing his first primary challenge since winning the job in the 1970s.
The Indiana GOP says it does not think the outcomes of Super Tuesday will affect its own presidential primary on May 8.
Political analysts say Governor Mitch Daniels will not be convinced to run for president.
Ryan says he will not endorse any candidates because he is head of the presidential campaign formation committee for the GOP.
The GOP is calling for an investigation to the claim that signatures on Obama and Clinton's 2008 petitions for presidency may have been forged.
With Indiana House Republicans making public their redistricting maps, several incumbents from both parties have been drawn together.