The emerging consensus is that Rick Santorum is the biggest threat yet to Mitt Romney. They have similar strengths, like a nice family and victories in blue states, notes Ramesh Ponnuru at Bloomberg View, but Romney has many of Santorum's weaknesses, only weaker. How can Romney portray Santorum as a fan of big government when he created the template for Obamacare? It appears voters increasingly find this argument persuasive. Here's our guide to today's polls and which ones matter.

Findings: Santorum is slightly ahead of Romney nationally, with 30 percent to 27 percent, respectively.
Pollster: CBS News/ New York Times
Methodology:  Interviews with 1,064 registered voters who said they'd vote in the Republican primary from February 8 to February 13.
Why it matters: On Monday, two polls showed Santorum and Romney tied; a third one with Santorum surging shows it's not a fluke. On January 20, Santorum had just 16 percent of the national vote, while Romney had only a teeny bit more than he does now, 28 percent. 
Caveat: In this race, the Not Romney leaders haven't lasted very long. Newt Gingrich's support has been cut in half since just before the South Carolina primary.

Findings: Obama is beating Romney in the general election 49 percent to 42 percent.
Pollster: Public Policy Polling; Rasmussen
Methodology:  Robocalls to 1,200 American voters from February 9 to February 12; robocalls to 500 likely voters over the last three days.
Why it matters: "One week before the Florida primary, Romney and Obama were tied," Rasmussen says. As many have noted -- and conservatives have fretted -- the negative ads Romney used to take down Gingrich didn't make voters like him any better. And they didn't wipe Gingrich's arguments from voters' minds either. "Coverage of Romney’s wealth, corporate history, and partially released tax situation coincided with, and almost certainly caused, a collapse in his support with white voters with income under $50,000," New York's Jonathan Chait writes. "Republicans have enjoyed great success attracting downscale whites in recent years, but that success has hinged in part on things like not nominating standard-bearers who epitomize everything blue-collar whites distrust about their party."
Caveat: PPP is a Democratic firm; Rasmussen leans right. And yet, the two come together with these findings.

Findings: Elizabeth Warren is slightly ahead of Scott Brown in the Massachusetts Senate race. 
Pollster: WBUR/ MassINC
Methodology:  Survey of 503 likely voters from February 6 to February 9.
Why it matters: Warren leads not necessarily because voters see her as a working class hero, as she has been portrayed. Only 17 percent think she comes from a middle class background. Brown is more likely to be seen as representing the needs of regular people by 33 percent to 30 percent.
Caveat: Brown is popular, with an approval rating of 50 percent.