(CNN) – The latest poll in Indiana's hard-fought Republican Senate primary shows Sen. Dick Lugar, the most senior Republican in the U.S. Senate, facing a ten-point deficit against his challenger Richard Mourdock.
With Indiana voters set to hit the polls on Tuesday, the Howey-DePauw University survey showed Mourdock at 48% and Lugar at 38%. Those figures included respondents who said they were leaning toward a candidate, as well as people who said they were firm in their choice.
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Just among voters who said they were firmly decided, Mourdock led Lugar 43%-35%.
Lugar, who is serving his sixth term in the Senate, has faced the toughest election battle of his career against Mourdock, Indiana's state treasurer. The incumbent been forced to defend his residency in the state, as well as his conservative bona fides against the tea party-backed Mourdock.
Asked why they were supporting Mourdock in Friday's poll, the most common response was that Lugar had been in office too long. Twenty-three percent cited Lugar's political longevity as the reason they were backing Mourdock, and 16% answered they thought it was time for a change. Fourteen percent said they just didn't like Lugar.
The Hower-DePauw University poll was taken by telephone from 700 likely Republican primary voters from April 30-May1. The sampling error was plus or minus 3.7 percentage points.