Former Massachusetts governor Mitt Romney won both of Tuesday's Republican primaries, sweeping Arizona and Michigan, with 47 and 41 percent of the vote, respectively.

Romney won all 29 delegates from Arizona under the state's winner-take-all system, and will net a substantial portion of the 30 delegates to be divvied up in Michigan.

Tuesday's victories -- rooted in the Romney campaign's strong organization in both states, the candidate's ability to outdo rivals in fund-raising and his performance at last week's Republican debate in Arizona -- are likely to revitalize Romney's push toward the party nomination.

They also set back the hopes of Rick Santorum, the former U.S. senator from Pennsylvania who had threatened to win Romney's birth state of Michigan.

With 99 percent of Michigan primary votes counted, Santorum had 38 percent to Romney's 41 percent, according to the Associated Press. In Arizona, where 89 percent of the votes had been tallied, Santorum also finished second, with 27 percent to Romney's 47 percent. Newt Gingrich and Ron Paul finished third and fourth in Arizona, but reversed that order of finish in Michigan.

While Arizona was an important win for Romney, it was in Michigan that Santorum's earlier primary victories posed a real threat to his status as presumed Republican front-runner. That role has been undermined and reasserted throughout the 2012 race.

The victories will provide an important boost for Romney, who before Tuesday had won primaries in four states -- New Hampshire, Florida, Nevada and Maine.

We didn't win by a lot, but we won by enough. And that's all that counts, the native Michigander told supporters Tuesday night in the Detroit suburb of Novi.

He didn't mention Santorum in his speech, instead criticizing President Barack Obama at length and trying to focus an economic message that some critics say has been muddled.

I'm going to deliver on more jobs, less debt, smaller government, Romney said. I'll make it simpler, smaller and smarter.

Santorum and former House of Representatives speaker Gingrich have won a total of five states.

Tuesday night, Santorum cast the close outcome in Michigan as a sign of success, noting that it came in Romney's back yard, the Washington Post noted.

A month ago, they didn't know who we are, but they do now, Santorum told supporters in Grand Rapids. The people of Michigan looked into the hearts of the candidates, and all I have to say is 'I love you back.'

Santorum avoided the kind of incendiary rhetoric that has drawn criticism in recent days - including an attack on Obama for being a snob for suggesting that young people should go to college. Instead, Santorum talked about small government and praised the women in his family for their hard work at home and in their careers. He spoke about how his mother had gone to college and received at least one advanced degree.

Arizona: Time and Patience

When it came to winning Arizona, Mitt Romney left nothing to chance.

Despite a likely victory in the state, the Romney campaign started early there, investing in organizational infrastructure while Santorum, Gingrich and Paul were focusing their attention elsewhere.

Romney's endorsement by John McCain, who took the state from Romney in 2008 -- and his endorsement by Gov. Jan Brewer only a few days ago-- helped seal his victory.

I think he's the man that can carry the day, Brewer told NBC's Meet the Press when she endorsed Romney. Mitt is by far the person that can go in and win.

Romney also had the advantage of campaigning in a state that, like Nevada, has a significant population of voters who share his Mormon faith.

According to a Public Policy Polling survey Sunday night, members of the Church of Jesus Christ of Latter-day Saints were expected to make up 14 percent of the primary turnout. Nearly 80 percent said that they were ready to cast their votes for Romney.

Bruce Merrill, a senior research fellow at Arizona State University's Morrison Institute for Public Policy, feels Romney's debate performance helped transform his victory over Santorum from a probability into a certainty.

Because the debate was held in Mesa, just days before Arizona's primary, Merrill believes that its impact was far greater than it would have been if it had been scheduled in the middle of February.

I think that the debate helped Romney here, Merrill told the Arizona Republic.

They put Santorum right on the defense, and he was on the defense the whole time on issues that do matter to conservatives.

For Jaime Molera, however, a Republican political consultant in Phoenix, it's all about the money, in Arizona, in Michigan, and in preparation for Super Tuesday.

Romney outspent Santorum in both states by about a 2-to-1 margin. The millionaire candidate's funds aren't running low yet.

I think Romney's money, at the end of the day, is going to propel him not just in Arizona but in all these other states, Molera said.

On Super Tuesday, you have all those states in play, and unless you have money and organization built up, it's just difficult to win.

That rosy outlook, however, would have been far less pointed if Mitt Romney had lost Arizona to Rick Santorum.

Michigan: The Long, Hard Haul

Only one month ago, it seemed that the primary race might soon be over.

Romney had swept Florida by roughly 47 percent of the vote, and he earned 50 percent of voters' support at the Nevada caucus only a few days later.

After a belated win by Santorum in Iowa, an upset victory by Gingrich in South Carolina and a groundswell of support for Ron Paul, Romney looked to be making good on the assumption that he would be the Republican presidential nominee.

Within the week, however, the chance to painlessly secure the GOP nomination was in jeopardy. And this was done by none other than Rick Santorum, a candidate many Americans assumed would be the next to leave the race.

Instead of quitting, the former Pennsylvania senator swept Colorado, Minnesota and Missouri in one night, suddenly threatening Romney's 123 delegates with 72 of his own.

Mitt Romney should have had a lock on the Michigan primary. It was the former Massachusetts governor's home state, one with fond memories of the candidate's father when the latter was governor from 1963 to 1969.

But after February's Santorum surge, the Romney campaign suddenly found its position in the blue-collar Northern state threatened.

In a final survey by Public Policy Polling, Romney and Santorum were in a statistical dead heat, with Santorum at 38 percent support and Romney at 37 percent.

The difference between the two was within the poll's margin of error, and the North Carolina firm advised that adding absentee ballots, which have given Romney an electoral boost in the past, would likely tip the scales in that candidate's favor.

Nonetheless, PPP found that support for Santorum was surging in the final hours before the Michigan primary began. The former Pennsylvania senator boasted 39 percent support to Romney's 34 percent on the second day of polling.

Momentum seems to be swinging in Santorum's direction, the firm concluded.

Santorum, when it comes down to it, is talking the talk and walking the walk, Republican State Sen. Jack Brandenburg, a Santorum voter, told MSNBC.

For him and Romney to be neck and neck in Romney's home state with the reputation that Romney's family has -- I think that says a lot for what Rick Santorum has done.

A loss in Michigan would have further hurt Romney due to the fact that the state held an open primary, giving Democrats and independents a chance to vote as well as registered Republicans.

Rick Santorum is by far the more socially conservative of the two, and a lot less likely to appeal to left-leaning voters. If Romney had lost despite all these advantages, he would have lost the one thing his campaign has relied upon throughout the campaign: the assumption that his nomination would be inevitable.

If Mr. Romney has trouble with blue-collar voters, doubts will deepen over whether he has the stuff in a one-on-one race in November to appeal to working-class voters in the states from Pennsylvania to Wisconsin, The Wall Street Journal reported this week.

Michael Falcone at ABC News put it more bluntly: losing Michigan would be Chernobyl.

Winning Michigan: Santorum Hit Hard

Instead, the Michigan loss is likely to add fuel to the fire that Santorum's front-runner status is anything other than what it has been for candidates like still-running Newt Gingrich and long-gone Herman Cain: a fluke.

Santorum has been struggling to make a good impression in recent weeks, never a good sign for a candidate propelled to front-runner status.

His debate performance in Arizona was lackluster at best. His social conservatism, meanwhile, while proof of his consistency, has resulted in soundbites that have offended everyone from college graduates to the entire Dutch press.

His positions, and his talking points, raise the question of whether he can appeal to women, to moderate Republicans and to independents, crucial demographics in 2012.

And while his three-state sweep was an impressive one, all his victories so far, except the non-binding and sans-competition Missouri primary, have been caucuses. Caucuses, while marked by the enthusiasm of those voting, are also known for the dearth of voters in general. They also tend to represent the most extreme parts of the party.

Santorum also finishes his double-loss having failed to get any endorsements from Michigan or Arizona. While these gestures of support can seem purely symbolic, they can also indicate what those in the know have on a particular candidate.

Endorsements ... are bets made by people with inside information, Jonathon Bernstein wrote in a piece for the Washington Post. The governors of Michigan and Arizona probably have someone they trust who has worked with Rick Santorum and has strong opinions about him. And what they're hearing, apparently, isn't anything good for Santorum.