Mitt Romney wins Maryland primary

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Mitt Romney began Tuesday night with an easy primary victory in Maryland, but his fate in Wisconsin--the biggest contest of the evening--remains unknown.

The Maryland race was called for Romney as the polls closed at 8 p.m ET. In D.C., which Romney is also expected to win Tuesday, Santorum did not appear on the ballot. Together, Maryland and the District have 53 delegates up for grabs. But Wisconsin--which will award 42 delegates--remains the major wild card and holds the potential to change the course of the primary race. Polls close in Wisconsin at 9 p.m. ET.

Wisconsin is a swing state that will factor heavily in the 2012 general election. If Santorum is able to best current delegate frontrunner Romney there, it could significantly boost Santorum's campaign going forward.

Santorum has pledged to remain in the race regardless of Wisconsin's outcome (He is spending Tuesday evening in Pennsylvania--his home state, which will hold its primary April 24.)

Even with a Wisconsin win, Santorum will remain significantly behind Romney in delegates, and will have the prospect of no additional wins in coming contests for the remainder of April (save in his home state of Pennsylvania--a must-win.) All of this comes as pressure ramps up for Santorum to bow out.

Leading up to Tuesday, Romney secured high-profile endorsements in Wisconsin from House Budget Chairman Rep. Paul Ryan and Sen. Ron Johnson.

The Romney campaign on Tuesday confirmed a Wall Street Journal report that it has formed a joint fundraising committee with the Republican National Committee for the general election. The move suggests Republicans are rallying around Romney even though the party extended the invitation to form a joint committee to all the GOP candidates running because the primary race is ongoing. Romney is the only candidate reported to have accepted.

The joint committee bumps the donation limit from $5,000 per donor for the primary and general combined to $75,000 via various related committees.

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