— Mitt Romney is dropping his recent focus on social issues and returning to his core message on the economy. After two weeks of talking about abortion, religious liberty and gay marriage to appeal to recalcitrant GOP conservatives ahead of Tuesday’s Michigan and Arizona primaries, Romney is signaling that he will leave those hot-button subjects to to the rival campaign of Rick Santorum in the upcoming states.

Santorum’s provocative comments on social issues have been roiling the campaign and attracting extensive media attention, but Romney is trying to frame the next stretch of the race around the economy.

Romney needs to rack up victories in the high-stakes Super Tuesday contests next week, especially in Ohio, where the two leading contenders are girding for a showdown. The GOP campaigns were looking ahead to the 10 states holding contests on March 6.

Romney appears to have concluded that he cannot beat Santorum on social issues, and that engaging in the fight may damage his general election chances if he is the nominee. So on Tuesday, Romney pivoted to assail Santorum for not campaigning enough on the issue voters say they care most about.

“It’s time for him to really focus on the economy — and for you to all say, ‘Okay, if the economy’s going to be the issue we focus on, who has the experience to actually get this economy going again?” Romney said at a rally in Rockford, Mich.

Romney offered himself as that candidate and sought to disqualify Santorum by calling him “a creature of Washington.”

But Santorum continued to press his argument that he would provide a sharper contrast to President Obama than Romney.

“We have an opportunity in this race to make this about Barack Obama and his failed policies,” Santorum told a breakfast of business leaders in the Detroit suburb of Livonia. “We need a candidate who can make that point, who can make it on the big issues of the day — energy, jobs, manufacturing, limited government, important issues like health care and its effect on the economy.”

The economy is comfortable issue turf for Romney and his advisers have long seen it as the path to both the GOP nomination and the White House. They say the plan is to carry that message into Ohio, where he is scheduled to campaign on Wednesday, as well as to Washington state, North Dakota and to delegate-rich southern battlegrounds like Georgia and Tennessee.

The Super Tuesday contests promise to be even more interesting with news Monday that an independent group supporting Newt Gingrich has received another substantial contribution from billionaire casino owner Sheldon Adelson and will launch TV ads in seven states of those states this week. A source close to the committee confirmed the donation on Monday, but did not confirm the amount. Adelson and his family have given two previous $5 million donations to the Gingrich group, Winning Our Future. The ads will launch in Georgia, Oklahoma, Ohio and Tennessee, Mississippi, Alabama and Kansas. The infusion could make Gingrich a factor again.

With polls showing the race between Romney and Santorum tight in Michigan, there was growing concern that Democrats may use the state’s open primary rules to make mischief in the GOP race.

Santorum’s ability to eke out a victory on Tuesday may lie with Democrats. There have been whispers for weeks about the impact Democrats could have in the primary, the idea being that they would vote for Santorum in a deliberate effort to deny Romney a victory.

The plot thickened when both President Obama’s campaign and a super PAC supporting Obama bought TV ads against Romney for opposing the auto bailout and the state Democratic Party sent an e-mail to supporters featuring video of a pair of Republican state senators urging Democrats to vote in the GOP primary.

“Clearly, there are prominent Democrats and liberal activists trying to stir things up,” said former Michigan GOP chairman Saul Anuzis, a Romney supporter. “If the election is close, they could distort the results and give Santorum a false sense of success.”

Henderson reported from Livonia, Mich.