Detroit (CNN) -- Mitt Romney will win the Michigan primary, CNN projected based on exit polls and partial returns, giving him a sweep of two contests Tuesday vital to his campaign for the Republican presidential nomination. Romney also is the winner in Arizona, according to the CNN projections, providing new momentum for the former Massachusetts governor in his bid to be the Republican candidate against President Barack Obama in November. In Michigan, Romney was ahead with 41% to 37% for Rick Santorum, 12% for Texas Rep. Ron Paul and 7% for Newt Gingrich, with 74% of unofficial returns counted. The state's 30 delegates will be allocated on a proportional basis, and Romney and Santorum each won three so far, according to the returns. However, it was unclear who would win the most Michigian delegates, which are based on congressional districts. Romney's victory in Arizona, where exit polls showed him getting 43% to 28% for Santorum, gave Romney all of the state's 29 delegates in the winner-takes-all primary. Trailing well back were Gingrich and Paul. Romney needed to win Michigan, where he grew up when his father was governor, to assert his ability to overcome the conservative challenge from Santorum. A Santorum victory in Michigan would have been a major upset, and raised more questions about how strong a candidate Romney is within his own party. Brokered convention a real possibility Early exit polls in Michigan showed frustration with the Republican field, according to those who responded to questioners. Less than half of voters in the Republican primary said they strongly favored their own candidate, while 52% had reservations or disliked the other candidate more, according to the exit poll data. Santorum launched automated phone calls Monday asking Michigan Democrats to vote for him in the open primary "to send a loud message to Massachusetts' Mitt Romney." In Michigan's primary, all voters can participate regardless of party affiliation. Liberal bloggers also have been asking Democrats and independents to vote for Santorum as a way of damaging Romney's chances of winning the nomination. Speaking to reporters in Livonia, Michigan, on Tuesday morning -- his first news conference in nearly three weeks -- Romney called the tactics by Santorum and Democrats "a real effort to kidnap our primary process." He called on Republicans to turn out "and say no to the dirty tricks of a desperate campaign." Santorum defended the calls to Democrats at a campaign stop Tuesday in Kentwood, telling CNN that Romney used the same tactics earlier when he encouraged New Hampshire voters to cross over to support him. A majority of voters in New Hampshire, which Romney won last month, were independents or Democrats, Santorum noted. "And when he goes out and recruits folks who aren't Republicans, that's all right," said Santorum, who later said of Romney: "That's what bullies do -- when you hit 'em back, they whine." However, it was Santorum who first complained of the crossover voting tactic in January, telling a Minnesota event that "We want the activists of the party, the people who make up the backbone of the Republican Party, to have a say in who our nominee is as opposed to a bunch of people who don't even identify themselves as Republicans picking our nominee." He called then for closed primaries with only Republicans allowed to take part "because it's the Republican nomination, not the independent nomination or the Democratic nomination." The exit poll information in Michigan showed one in 10 respondents were Democrats voting in the GOP primary, while six in 10 were Republicans and the rest were independents. More than half of the Democrats backed Santorum, while Romney was ahead among Republicans and the two were tied among independents, the exit polls showed. Democrats who voted Tuesday said they didn't need much convincing to support Santorum in order to weaken Romney. "I said, 'Why not? This is my way of voting,'" Dearborn Heights resident Gary Zulinski said. "That's my right. There are so many people who don't exercise that right. This is my way of saying 'Hey, I've had enough.'" Bruce Fealk, another Democrat, said he voted for Santorum because "he's by far the weakest candidate." The idea is to help Obama get re-elected, Fealk told CNN, adding: "We want Mitt Romney to go bankrupt in Michigan." Democratic strategist Joe DiSano, who mounted the Democrats-for-Santorum effort, said he had commitments from 14,000 people to vote Tuesday and predicted they would leave the Republican National Committee drinking "Pepto-Bismol by the gallon." Crystal Larson, another Dearborn Heights Democrat, said her vote for Santorum made her "feel like I made a deal with the devil." "Voting for Santorum goes against everything I believe in and everything I've ever stood for in my life," Larson said. "And to vote for him takes a lot of guts, I think." Romney attributed Santorum's late rise in the polls to his recent "incendiary comments" about President Obama. "We have seen throughout the campaign that if you are willing to say really outrageous things that are accusative and attacking of President Obama, that you are going to jump up in the polls," Romney said. "You know, I am not willing to light my hair on fire to try and get support. I am who I am." The tough talk reflected the high stakes in Michigan. Romney has led nationwide polls off-and-on over the course of the campaign, but has been unable to increase his support base. Santorum is the latest of Romney's rivals to challenge him for front-runner status by playing on conservatives' reservations about the former Massachusetts governor. Santorum's hat trick earlier this month propelled him to a lead in national polls and a double-digit lead in Michigan two weeks ago. But he had a lackluster performance in last week's CNN/Arizona Republican debate and has fallen into a statistical tie with Romney in national polls and in Michigan. Zelizer: For Republicans, social issues are losers Both candidates have been spending most of their time in Michigan following the last debate, and Republican strategist and CNN contributor Alex Castellanos said a Romney victory there would greatly boost his campaign. "In Michigan, Romney has brought Santorum down from a double-digit lead to a few points in his wake. If Romney wins in Michigan, there will be no opponent left he hasn't defeated one-on-one," Castellanos said earlier in the day. "In the year of the comeback, it may turn out that the king of the comebacks is Mitt Romney," said Castellanos, who was a top media adviser for Romney's 2008 nomination bid but who is not taking sides this cycle. Michigan and Arizona come four days before Washington state holds its caucuses on Saturday and a week before 10 states hold primaries and caucuses on Super Tuesday. "If Romney wins Michigan, he can suffer a few losses on Super Tuesday and still take the nomination," Castellanos said. Gentry Collins, a former political director for the Republican National Committee and the Republican Governors Association, said a Romney loss in Michigan would be a public relations problem for his campaign, but that it wouldn't fundamentally change the dynamic of the campaign. Meanwhile, Santorum adviser John Brabender, who has been downplaying expectations for his candidate in Michigan, noted that the 30 delegates at stake there are proportional, so a second-place finish with a decent delegate haul is just as good as a win. To Brabender, Santorum already has won by forcing Romney to spend major campaign resources in a state considered home turf. "The Romney campaign is spending a fortune they never expected to spend in Michigan, and every dollar they spend in Michigan is a dollar they don't have on Super Tuesday," Brabender told CNN on Monday. While Michigan is getting inundated with advertising spots, Arizona's airwaves are less cluttered with campaign commercials. "It confirms most observers' assessments from polling and fundraising reports: Michigan is the more competitive race of the two and that the campaigns have to triage their resources for what could be a primary campaign that continues well beyond these late February contests," said Kenneth Goldstein, CNN's consultant on TV advertising and president of Campaign Media Analysis Group, a company that tracks and estimates the costs of campaign ads running on the air. The most recent polls indicate Romney with a single-digit to a double-digit lead over Santorum in Arizona, with Gingrich and Paul further behind. Since Arizona's 29 delegates are winner-take-all, neither Gingrich nor Paul has spent much time in the state. Arizona's primary allows Republicans and independents, but not Democrats, to participate. Early voting in Arizona began February 2, and officials say about half of those eligible to vote in the primary will have already done so by Tuesday. For Gingrich, it's all about Super Tuesday and Georgia, which he represented in Congress for more two decades. "I want to focus on winning in Georgia. I think it is essential to us to do that, and we are going to do everything we can between now and next Tuesday to win here at home," Gingrich said last weekend while campaigning in the state. However, Gingrich's hopes of building a strong support base in the South after his lone victory in South Carolina appears in trouble. Santorum holds a big lead in polls in Tennessee, another Super Tuesday state. For Paul, the longtime congressman from Texas who's making his third bid for the White House, Arizona is an afterthought. Paul campaigned briefly in Michigan, where he'd like to pick up some delegates, but mostly he's looking ahead to Washington state and Super Tuesday caucuses, when he hopes to increase his delegate count.