Mitt Romney this morning significantly increased his criticism of his chief rival Rick Santorum, offering an economic critique after several days spent trying to bolster his credibility among social conservatives. With polls showing a dead heat in this crucial battleground state, Romney is hoping to prevent an embarrassing defeat in his native state that would further upend a Republican nominating contest that has been marked by its volatility. Santorum is hoping to shock the political establishment by beating Romney here and sowing fresh doubts over the former Massachusetts governor’s ability to win over social conservatives and blue-collar workers.