By the end of April we may have a Republican nominee for president. Republicans are coalescing around Romney, as he has picked up recent endorsements from party leaders past (George H.W. Bush), present (Jeb Bush, Paul Ryan) and future (Marco Rubio). Meanwhile the primary calendar is set to give the frontrunner a boost this week.

The widespread perception is that Romney has had the steady backing of the GOP establishment. In fact, it appeared that way only because his opponents were so unappealing, or even unserious, in the eyes of most influential Republicans, that they received even fewer endorsements. By historical standards Romney has actually lagged behind past favorites. As BuzzFeed’s Zeke Miller notes, “George W. Bush locked up 44 Senate endorsements before the South Carolina primary, and had more than half of the House’s 222 Republicans backing him by May of 1999—well over a year before the election. But to date, Mitt Romney has only gathered the endorsements of 91 Republican members of Congress—including just 17 senators.”  

On Tuesday Maryland, Wisconsin and Washington, D.C., will hold their primaries. Washington is considered such friendly territory for Romney that Santorum’s campaign claims he will be no worse off for not having even gotten onto the ballot. Maryland, being a liberal Northern state, is also Romney country. The Washington Post reports, “the often overlooked and bulging moderate middle of the Maryland GOP will be relevant—at least for a day. In the state’s first competitive presidential primary in a generation, polls and interviews suggest an overwhelming number of Republicans will vote for Mitt Romney.”

Santorum’s only chance at slowing Romney’s momentum will be in Wisconsin. Santorum has been competitive in industrial MidWest, but he has yet to score a decisive win there. MidWestern states have competing characteristics, some of which favor Romney and some Santorum. They tend to have lower education and income levels than the Northeast. That helps Santorum, who does better with less wealthy and educated voters. But they have fewer evangelicals than the South, Great Plains and Rocky Mountain West. Generally, Santorum only wins in states where evangelical or born again Christians are a majority of Republican primary voters.

Romney is following his standard playbook in Wisconsin and massively outspending his opponents. His Super PAC, Restore Our Future, has spent $2,687,938, compared to $735,093 from Santorum’s Red White and Blue Fund.

Polls show Romney leading Santorum by an average of seven or eight points in Wisconsin. The New York Times’ statistical guru Nate Silver gives Romney a 91 percent chance of victory.

After Tuesday Santorum’s last stand will be the April 24 Pennsylvania primary. The other states to vote on April 24—Delaware, New York, Rhode Island, Connecticut—are likely to favor Romney. Santorum has conceded that he must win his home state to stay viable. If Romney is able to win Pennsylvania and sweep the April primaries, the nomination could be settled and pundit fantasies of a brokered convention in Tampa would be an ancient memory by August.