Gallup national tracking poll - March 1 through March 31st
The months of wild mood swings in the national polls are over. The trends this month are pretty steady.
Mitt Romney: the clear front runner has climbed from hovering about 35% to hovering around 40%
Rick Santorum: He was just under 25% at the beginning of the month and has climbed a little, but 30% is right now a barrier for him.
Newt Gingrich: A slow leaking tire. Early in the month he wobbled a few points under or over 15%, but now he is much closer to 10%.
Ron Paul: The most consistent support of all the candidates since the beginning of the year, he flirted with 8% for a few days - a tie for his lowest ebb this year - but is now holding stead at 10%
None of the Above: See Newt Gingrich. It may not be precisely correct, but the loss of support for Gingrich and NOTA looks to have been accumulated by Romney and Santorum, slightly more for Mitt than for Rick.
The delegate count is at about the halfway point. Romney has a big lead and his lead will likely stretch on Tuesday barring a couple more weird primaries where Santorum's support is underestimated wildly. Right now it looks like a sweep of Wisconsin, Maryland and DC for Mitt, and even if he only takes two of three, the slow accumulation will continue.
As I have said before, the metaphor isn't the knockout punch but a boa constrictor killing some large animal then digesting it. It's not exciting, but if it's not inevitable, it's as close as anything gets.