A new Pew Research Center poll found Santorum and Romney neck-and-neck, with Santorum winning 30 percent of the support among Republican registered voters to Romney's 28 percent — a difference that falls well within the poll's five percentage point margin of error. Separately, Gallup's latest tracking survey of the Republican race found Romney with 32 percent support and Santorum right on his heels with 30 percent.  Santorum also polls neck-and-neck with Romney in Romney's home state of Michigan.

What is to explain this?

As I have written here before, Santorum has been running a great campaign on a shoestring budget.  While everyone was watching the debates to see whether Newt would beat up Mitt (or vice versa), Santorum did a great job of establishing himself as the true conservative (unlike Mitt) who can remain reasonable (unlik Newt).  It has finally paid off, and last week's caucus wins made people realize that he is a viable candidate.

Santorum's problem, of course, is that he is far too conservative to win against Obama.  Whenever he opens his mouth about social issues, he loses independents.  And he's opening his mouth a lot nowadays — on gay marriage, on contraception (are we really debating this issue in 2012?!?).

Romney will be, as I have always said, the GOP nominee.  But Santorum shoul enjoy the next couple of weeks.  It's the closest he'll get to the White House.