(CNN) -- The economy was foremost on voters' minds Tuesday as they cast their ballots in the primaries in Michigan -- a state with one of the highest unemployment rates in the country.
Voters in both the Republican and Democratic primaries in Michigan ranked the economy as the top issue.
More than half of Republican voters ranked the economy as the most important issue, exit polls showed.
About 41 percent of those for whom it was the top concern cast their ballots for former Massachusetts Gov. Mitt Romney, compared with 29 percent for Arizona Sen. John McCain.
Michigan's economy is powered by the automotive industry, which has been struggling.
During the campaign, Romney said he believed he could bring back lost jobs and pledged that in the first 100 days of his presidency, he would convene a summit to rebuild the Big Three automakers.
McCain, on the other hand, said many of the auto industry jobs were gone forever and vowed to focus instead on retraining for jobs of the future.
Romney's was the much more "activist, 'I get Michigan' " message, said CNN's John King. Watch King analyze the Michigan results »
On the Democratic side, 61 percent rated the economy as the most important issue in the Michigan primary, and more than half of those voters cast their ballots for Sen. Hillary Clinton -- the only top-tier Democrat on the ballot.
She also received almost half the votes from those who rated Iraq as the top issue in the Democratic primary.
About 40 percent of those who considered Iraq the most important issue on the Republican side voted for McCain, compared with 29 percent for Romney, exit polls showed.
But those who said they strongly approved of the war went for Romney 43 percent, to 21 percent for McCain.
Ideology was key in the Republican primary, with conservatives helping propel Romney to victory in Michigan.
About 40 percent of those who identified themselves as conservative in exit polls said they voted for Romney, compared with 22 percent for McCain.
"Probably one of the most devastating problems John McCain had was among conservatives -- the base of the Republican party," said CNN senior political analyst Bill Schneider.
"The indication is they still don't trust McCain, they've disagreed with him on too many issues. He lost the base of the Republican party. Romney is the conservative favorite, that's how he won."
Almost half of those who said they felt enthusiastic about the Bush administration voted for Romney, compared with 16 percent for McCain.
McCain won Michigan in 2000 by convincing independents and even Democrats to vote for him in the GOP primary. Independents voted for McCain once again Tuesday, but there weren't enough of them, Schneider said.
"They just didn't turn out this time in the same large numbers," he said.
Romney's ties to Michigan also played a role. Both the former Massachusetts governor and his wife were born in Michigan, and his father was governor of the state in the 1960s.
About 42 percent of those who voted in the Republican primary said those Michigan ties were either very or somewhat important, exit polls showed. E-mail to a friend
CNN's John Roberts contributed to this story.