WASHINGTON — Mitt Romney scored a hard-won, home state triumph in Michigan and powered to victory in Arizona on Tuesday night, gaining a two-state primary sweep over Rick Santorum and precious momentum in the most turbulent Republican presidential race in a generation.
"We didn't win by a lot, but we won by enough," Romney told cheering supporters in Michigan. He also tweeted his delight — and his determination: "I take great pride in my Michigan roots and am humbled to have received so much support here these past few weeks.
"On to the March contests," he said, looking ahead to next week's Super Tuesday races that could go a long way toward determining the Republican who will take on Democratic President Barack Obama this fall.
Santorum was already campaigning in Ohio, one of next week's states, when the verdict came in from Michigan.
"A month ago they didn't know who we are, but they do now," he told his own supporters, vowing to stay the conservative course he has set.
The two other candidates, Newt Gingrich and Ron Paul, made little effort in either Michigan or Arizona, pointing instead to next week's collection of contests in all corners of the country.
Romney's Arizona triumph came in a race that was scarcely contested, and he pocketed all of the 29 Republican National Convention delegates at stake in the winner-take-all state.
Michigan was as different as could be — a hard-fought and expensive battle in Romney's home state that he could ill afford to lose and Santorum made every effort to win.
Returns from 88 percent of Michigan's precincts showed Romney at 41 percent and Santorum at 38 percent. Paul was winning 12 percent of the vote to 7 percent for Gingrich. In Arizona, with votes counted from 64 percent of the precincts, Romney had 48 percent, Santorum 26 percent, Gingrich 16 percent and Paul 8 percent.
In Michigan, 30 delegates were apportioned according to the popular vote. Two were set aside for the winner of each of the state's 14 congressional districts. The remaining two delegates were likely to be divided between the top finishers in the statewide vote.
With his victory in Arizona, Romney had 152 delegates, according to The Associated Press' count, compared to 72 for Santorum, 32 for Gingrich and 19 for Paul. It will take 1,144 supportive delegates to win the nomination in August at the Republican National Convention in Tampa, Fla..
In interviews as they left their polling places, Michigan voters expressed a notable lack of enthusiasm about their choices. Just 45 percent said they strongly favored the candidate they voted for, while 38 percent expressed reservations and 15 percent said they made the choice they did because they disliked the alternatives.
The lengthening GOP nomination struggle has coincided with a rise in Obama's prospects for a new term. A survey released during the day showed consumer confidence at the highest level in a year, and other polls show an increase in Americans saying they believe the country is on the right track.
Along with the improving economy, the long and increasingly harsh campaign, in which Gingrich and Santorum have challenged Romney as insufficiently conservative, has prompted some officials to express concern about the party's chances of defeating Obama in the fall.
Romney signaled he intends to stick to his core campaign message of fixing the economy and reducing unemployment in a nation still recovering from the worst recession in decades.
"More jobs, less debt and smaller government — you're going to hear that" over and over in the states ahead, he said.
Exit polling showed a plurality of Republican voters in both Michigan and Arizona saying the most important factor to them in the primaries was that a candidate be able to beat Obama in November. Romney won that group in Michigan, where it mattered most, and he also prevailed among voters in the state who said experience was the quality that mattered most.
Santorum ran particularly well among voters who cited a desire for strong conservatism or strong moral character.
The polls surveyed both primary day and absentee or early voters. Interviews were conducted at 30 polling places in each state. Early results from Arizona's poll included interviews with 1,617 voters, including 601 absentee or early voters interviewed by phone. In Michigan it was 2,133 interviews including 412 absentee or early voters interviewed by telephone. The margin of sampling error for both polls was plus or minus 4 percentage points.
The primaries in Michigan and Arizona were the first contests since Romney squeaked out a victory over Paul in the Maine caucuses on Feb. 11, a lull of two and a half weeks.
Except for a debate in Arizona on Wednesday and a brief burst of campaigning in the hours before and after, Romney and Santorum have focused their time and campaign money on Michigan.
Polls showed Santorum racing to a large advantage after his victories on Feb. 7, before the weight of attack ads by a Romney-aligned super PAC and the candidate himself began to narrow and finally erase the gap in many surveys.
In the end, the combination of Romney and the political action committee accounted for about $3.8 million in TV ads, compared to about $2.2 million for Santorum and a super PAC supporting him.
While that gave Romney an advantage, it wasn't nearly as lopsided as in some of the earlier states.