“It looks like things in Michigan are swinging back toward Rick Santorum in the final hours before the polls open,” said Dean Debnam, president of Public Policy Polling, in a statement. “The big questions are whether Romney’s absentee vote lead is too large for Santorum to make up, and whether Democrats really will turn out to support Santorum in the GOP primary.”

But a Mitchell/Rosetta Stone poll released Tuesday showed those results flipped, with Romney holding a one-point edge. In that poll, Romney earned 37 percent, Santorum 36 percent, and Paul and Gingrich were tied with 9 percent each.

Rosetta Stone is the same polling firm that found Santorum with a two-point edge over the weekend when most polls showed voters shading towards Romney, meaning that the former Massachusetts governor has gained ground in their measure. So while PPP shows the momentum favoring Santorum, the pollsters at Rosetta Stone are seeing Romney gain strength.

“The lead changed again in a race that appears to be very, very close. Romney leads by just 1.4 percent on the eve of the election. The big change in tonight’s polling seems to be an increase in support among women voters where Romney now leads by 5%. Depending on the turnout, the race could go either way,” Steve Mitchell, president of Mitchell Research & Communications, said in a statement.

However the data is sliced, Michigan looks likely to come down to the wire. 

Nate Silver, who analyzes polls for The New York Times, says that his model would give Mitt Romney a 55-45 percent chance of winning, with a lead likely to consist of less than 1 percentage point. That's a tenuous advantage, and one Santorum could easily overcome with a strong turnout.

Still, Romney was confident Monday on Fox News, predicting a win in both Michigan and Arizona, which also votes Tuesday and where he has held a steady lead in the polls.

“I’m planning on winning here in Michigan and also in Arizona,” Romney said. “Obviously, that will be huge for us if we’re able to do, particularly having come from so far behind here in Michigan.”