Some of Mr. Lugar’s critics accused him of being Mr. Obama’s closest Republican friend — a claim Mr. Lugar scoffed at, but also took questions about right up until Tuesday afternoon. They also railed against positions he took at various times in favor of Mr. Obama’s Supreme Court nominees, the Dream Act, the bank bailout, the nuclear arms control treaty and more.

Mr. Lugar’s supporters countered that he had maintained a conservative agenda over the years, for less government spending, a balanced-budget amendment and fewer regulations that harmed businesses.

For his part, Mr. Lugar sounded unbowed on Tuesday afternoon, arguing that most Americans were fed up with partisan battling and saying his race had evolved into a “playground” for outside interest groups.

If it felt peculiar to be entering an election day as an underdog — Democrats did not even field an opponent six years ago — Mr. Lugar did not show it. “This morning, I woke up after a good night’s sleep, just as before, ready with vim and vigor to make certain that we do the Lord’s fight today, and we’re going to do the best we can,” he said.

But for some here, Mr. Lugar’s troubles reached beyond questions of partisan loyalty. He was required this year to change his voter registration to the farm his family has owned for years rather than the Indianapolis house he sold in 1977 — an episode that underscored how long he had been in Washington and, in the view of some, how tenuous his ties to Indiana now felt.

“Everybody’s time comes,” said Ed Budd, who described himself as a Tea Party supporter and handed out Mourdock leaflets outside a polling place in Fairland on Tuesday when Mr. Lugar walked up looking, in Mr. Budd’s words, “diminished some” from the familiar image he had seen on television for so many years.

Throughout the day, voters for and against Mr. Lugar confided quietly that they felt sadness and discomfort as they witnessed the unfolding scene.