Former Massachusetts Governor Mitt Romney took a big step toward locking down the GOP presidential nomination on Tuesday when he pulled off a clean sweep of the day's three primaries. With decisive victories in Wisconsin, Maryland and the District of Columbia, Romney appeared to finally vanquish his rivals as he increasingly turned his attention to President Obama. Romney won 42.5 percent of the vote in Wisconsin, outpacing his only remaining threat, former Pennsylvania Senator Rick Santorum, who earned 37.6 percent. Ron Paul and Newt Gingrich were well behind both men in all three contests. In Maryland, Romney took 49.1 percent to Santorum's 28.9, and in Washington, D.C., Romney landed a commanding 70 percent to Paul's 12 and Gingrich's 11; Santorum was not on the ballot in D.C.

"This has really been quite a night. We won a great victory tonight in our campaign to restore the promise of America," Romney said.

"President Obama thinks he's doing a good job — I'm not kidding," he told a crowd in Milwaukee while standing in front of a large American flag, according to the New York Times. "It's enough to make you think that years of flying around on Air Force One, surrounded by an adoring staff of true believers telling you that you're great and you're doing a great job, it's enough to make you think that you might become a little out of touch."

After once again slamming the president for creating what he deemed a "government-centered society" based on bloated White House policies, Romney promised his followers that he would preside over a different America if he wins in November. "The dreamers can dream a little bigger, the help wanted signs can be dusted off, and we can start again," he said. "And this time we'll get it right."

Romney now has 58 percent of the delegates needed to secure the nomination, but his slow, methodical march to the magic number of 1,144 is not quite over, as Santorum vowed that he would stay in the race through the April 24 primaries. Five states will vote on that day, including his home state of Pennsylvania, where Santorum believes he can put up a convincing victory that might pave the way to more wins in May.

According to estimates, Romney has 648 delegates so far to Santorum's 264.

Even before Romney could celebrate, he got a taste of what the general election might feel like when President Obama singled him out for some criticism while speaking to a crowd of editors and reporters in Washington. Obama slammed Romney for supporting a GOP budget proposal that the president likened to "social Darwinism."

"He said that he's 'very supportive' of this new budget," Obama said of Romney, before seeming to mock his potential challenger's one-percent pedigree. "And he even called it 'marvelous,' which is a word you don't often hear when it comes to describing a budget ... it's a word you don't hear generally." He assailed the budget plan put forward by House Republicans for slashing funding for education and infrastructure in favor of more tax breaks for the wealthy.

The fiery speech came on the same day that Obama clinched the uncontested Democratic presidential nomination with wins in all three states.

With Santorum (not to mention Gingrich and Paul) showing no signs of leaving the GOP contest, pundits predicted that the road ahead for Romney could still be tough, as he must continue to beat back the other contenders in some Southern primaries in May while attempting to focus his fire on Obama.

Stick with MTV's Power of 12 throughout the presidential election season for updates and news from the campaigns.