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Santorum has been facing some pressure from Republicans to drop out of the race and allow Romney to become the party’s nominee.  Pressure would increase if Romney wins Wisconsin.

The victory would give Romney a large lead in delegates as well.

The Public Policy Poll shows Romney beating Santorum among conservative and Tea Party members, a former Santorum stronghold.

"Increasingly Mitt Romney is eating into Rick Santorum's base," Dean Debnam, president of Public Policy Polling, told Reuters. "That would seem to be a sign GOP voters are ready for this race to be over."

Romney is now preparing to take on Barack Obama in the general election, donors told the NY Times. His campaign is also reportedly expanding its Boston headquarters and building operations across the country. Romney has also been looking to add more seasoned advisors to his campaign.

Santorum, however, is not giving up on his bid to become the Republican presidential candidate and has urged the party to let him, a stronger conservative candidate, fight Obama in the general election.

The union vote could be a very powerful determining factory in the primary Tuesday. Wisconsin has an incredibly strong labor movement, according to St. Louis Today. Several unions have their state headquarters in Milwaukee.

There is currently a fight over the cost of public worker benefits during difficult economic times.

Unions in Wisconsin forced Republican Gov. Scott Walker into a recall election after his aggressive first-term and efforts to eliminate public employee’s unions’ power. The power of unions in Wisconsin is indeed going to be a strong factor in the primary and may be one reason Romney is fairing better in the polls then the more conservative Santorum.

Rep. Paul Ryan of Wisconsin endorsed Romney on Friday. Ryan is the chairman of the House Budget Committee.

It is unclear how much Ryan’s comments earlier this week that U.S. generals didn’t support Obama’s Pentagon budget, and subsequent apology, will effect how influential his endorsement is.

Regardless, Romney is expected to receive half the total delegates needed to win the nomination this week.

A Republican has not carried Wisconsin in the general election since 1984, but the party hopes to change this.