It's been a strong week for the Mitt Romney campaign. Over the past couple of days, the candidate creeped up in the polls and took back the lead from Rick Santorum.
"The momentum certainly seems to be on the Romney campaign side," said political analyst Tom Shields.
Shields says this change is partly because Romney's investment in campaign ads is working.
"Romney spent about $6 million - $6.5 million in advertising in the last two weeks here," Shields said.
About one third of that money was spent on ads against Santorum.
"So he out spent Santorum by nearly two to one here on advertising. Some of that negative going after the Santorum record, trying to define who Santorum was, not quite as conservative as you think so," Shields said.
According to Shields, Romney also outperformed Santorum during Wednesday's debate and put himself in favor with conservative voters.
"Romney did a good job in laying out the fact he's conservative on spending, he's conservative on all these programs they wanted about turning back Obamacare," Shields said.
Pollster Bernie Porn also thought Santorum did not do so well.
"His explanation for supporting his home senator who's not considered conservative...just was not well done at all," Porn said.
However, Romney's lead in the polls is considered marginal and the outcome of Michigan's GOP primary is still unpredictable.