I’ve previously looked in detail at the breakdown of GOP primary votes here, here and here; for purposes of this series, I’ve broken out the votes in three groups – the five conservative candidates (Santorum, Gingrich, Perry, Bachmann and Cain), the two moderate candidates (Romney and Hunstman) and the libertarian (Paul) – for reasons explained in the first post. In my second post, I detailed the signs to look for to see whether and when Romney would start putting the race away with the voters rather than simply plodding through the accumulation of delegates.

After the March 24 vote in Louisiana and Tuesday’s votes in Wisconsin, Maryland and DC, we can see the signs of that momentum shift, but only slightly, with stubborn resistance to Romney still continuing. Not-unrelatedly, we can see the collapse of Newt Gingrich’s campaign to levels even lower than he was getting in February, the last time he went a month without being on the ballot in any Southern state (recall that Newt was not on the Missouri ballot). Let’s start with the month-by-month running tally:

This looks like a significant shift to Romney after the deterioration of his numbers in March, but as with his rough showing in March, you have to bear in mind the calendar: all three primaries on Tuesday were in blue territory (deep blue in the case of Maryland and DC, plus Santorum wasn’t on the ballot in DC, whereas Wisconsin has been much more favorable lately to Republicans, with Tea Party-backed Republicans Ron Johnson and Scott Walker winning statewide in 2010). The real dynamic remains mostly the same, with Romney’s supporters and opponents just not evenly distributed geographically. Let’s update the red/blue/purple numbers, previously broken out here, again excluding Virginia because none of the conservatives were on the ballot:

As you can see, the vote totals for April are actually slightly more favorable to the conservatives in general, and less favorable to Romney, than the overall blue-state numbers. That’s not to say that Romney underperformed, per se; Santorum had been leading him in Wisconsin until the campaign and its related advertising blitz started there in earnest after Louisiana, and while Romney had won narrow primary victories in Michigan and Ohio, Santorum had previously won caucuses in Minnesota and Iowa. So, Wisconsin was far from a natural gimme for Romney, and his win there – while hardly overwhelming, with he and Huntsman still combining for less than 45% of the vote – can’t be ascribed solely to being on blue turf. Sean Trende went in more demographic detail the day before the vote to explain why Wisconsin could be a sign of momentum shift. On the other hand, Romney was unable to muster a majority in deep-blue Maryland, where John McCain won almost 55% of the vote against Mike Huckabee on February 12, 2008; McCain also won almost 55% a week later in Wisconsin. Thus, the break to Romney is happening at the margins, and is not yet the stampede that McCain was enjoying by mid-February in 2008, when a smaller bloc of social conservative voters were holding out for Mike Huckabee (McCain would go on to win majorities in Texas, Ohio, Vermont and Rhode Island on March 4 before Huckabee dropped out). The sense that Romney is winning over the objections of a majority of the party’s voters will not be dispelled any time soon; the best he can hope for is a determined resignation to put the primary slog out of its misery and move on to the general election.

The collapse of the Newt campaign may also be overstated somewhat here (he’s been getting clobbered in the blue states all year), but there really seems to be no life left in Newt’s cash-strapped operation besides protest votes (full disclosure: I cast a vote yesterday for Newt by absentee for New York’s April 24 primary, purely as a protest; I might have voted for Perry if he’d been on the ballot). Amusing, neither-here-nor-there detail: with Perry and Cain not on the ballot, Michele Bachmann actually drew more votes in Wisconsin than she has in any other state, 8 more than she got in Iowa.

Finally, let’s update the state-by-state tally – Virginia and DC are marked with asterisks because of the absence of major candidates from the ballot, Guam and American Samoa are excluded because I couldn’t find popular vote totals:

It’s nearly three weeks until the next set of primaries on April 24, all in the deep-blue Northeast (New York, Connecticut, Rhode Island and Delaware) except for blue Northeast/Midwest hybrid Pennsylvania, where Santorum – as the hometown favorite son – looks to make his last stand. Santorum trails badly in the polls in all of them besides Pennsylvania, where the polls are moving against him. The others should be be easy wins for Romney even without a momentum shift, but if Santorum loses Pennsylvania, it should convince Santorum – and Gingrich, who should have already – to throw in the towel and admit that, whether the voters like it or not, Mitt Romney is the 2012 GOP presidential nominee.