Rick Santorum’s convincing wins in Tuesday’s Deep South double-header shook up the GOP presidential primary contest once again, highlighting frontrunner Mitt Romney’s chronic weaknesses among conservatives while raising questions about Newt Gingrich’s ability to remain a major force in the nominating race. The conservative underdog, Santorum can now lay greater claim to being the strongest challenger to Romney, who fell to 0-for5 in the crucial southern region of the country. In January, South Carolina voters stifled his momentum after New Hampshire. Tennesseans gave Santorum a victory on Super Tuesday last week that once again showed Romney lacked appeal among white, evangelical Christians.