The opposition is also about policy and personality.
Conservative groups take issue with Hagel's policy positions, but also, "They don't like the fact that he is a supporter of President Obama," said Andra Gillespie, an associate professor of political science at Emory University in Atlanta.
"Republicans have been playing opposition politics for four years and it's not easy to come out of that mold," he said. "In Hagel's case there's no love lost. They see him as someone as who turned on his party and they don't want there to be any confusion that this is a real Republican going into the Obama Cabinet."