A third national poll has now shown former Senator Rick Santorum (R-PA) with a lead in the Republican primary race. A new survey commissioned by CBS News and the New York Times shows Santorum with 30 percent of GOPers, followed closesly by former Massachusetts Gov. Mitt Romney at 27, Rep. Ron Paul (R-TX) with 12 and former House Speaker Newt Gingrich has faded to the back with 10 percent. Santorum’s lead is within the margin of error, and therefore he and Romney are locked in a statistical dead heat.

Public Policy Polling (D) data showed Santorum with a 15 point lead this weekend and Pew numbers on Monday showed him with a two point advantage. The CBS/NYT analysis found a familiar pattern – the very conservative bloc in the Republican Party is driving the non-Romney contingent: 

The poll is the latest example of the tremendous instability that has marked the Republican nominating contest, in which candidates have repeatedly shot up in popularity and then plummeted.

Mr. Santorum’s bump is largely fueled by increased support from self-described conservatives, evangelical Christians and Tea Party supporters. The poll shows Mr. Santorum, a former Pennsylvania senator, backed by nearly four in 10 voters from each of these groups; last month, no candidate was the clear favorite among these voters.

Our TPM Poll Average now shows Santorum with a slight lead nationally.