But Indiana voters have a penchant for split tickets and many are more accustomed to the buttoned-down Midwestern style of Republicanism evinced by the reserved Lugar, the former mayor of Indianapolis, and Daniels, a former corporate executive, than that of the brash Mourdock.
Polls indicate many voters were offended by Mourdock's slashing attacks on Lugar, even those who thought it was time for the 80-year-old senator to retire. In a statement, Lugar fed those doubts by saying Mourdock's hard-line approach is "not conducive to problem solving" and would be a ticket to failure as a lawmaker.
When the general election campaign revved up last month, a new Mourdock emerged with a milder message, bonding himself to Daniels and to well-known Republican surrogates such as Lt. Gov. Becky Skillman and Oklahoma Sen. Tom Coburn.
The transformation has left some Republicans shaking their heads.
"The night of the election he was singing the tea party's praises — 'I couldn't have gotten elected without the tea party!' — and then the clock turned midnight and he's a mainstream Republican," said Mike Murphy, an Indiana Republican strategist and former state representative.
Lugar supporter Anne Emison Wishard said Mourdock's change seems mostly cosmetic.
"I smell panic," said Wishard.
But Joe McKinney, a 59-year-old education professor at Ball State University who voted for Lugar, said the mainstream endorsements have made a favorable impression. They are "more moderate Republicans who seem interested in the issues I'm interested in," he said.
Donnelly says Mourdock's recent appearance at a tea party event in Texas with commentator Glenn Beck showed his true stripes and undercut his "ability to come back and talk to Hoosiers in the middle." Several prominent Lugar supporters have raised money or hosted meetings for Donnelly.
But Monica Boyer, co-founder of the tea party umbrella group Hoosiers for a Conservative Senate, said Mourdock's different messages don't worry her.
As for Donnelly, she said, "He could campaign with Mother Teresa and he would still have 'Obamacare' stamped on his forehead."
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