Republican presidential upstart Rick Santorum found himself under increasing scrutiny on Thursday as front-runner Mitt Romney tried to chip away at his credibility ahead of the key New Hampshire primary. Santorum's surge in Iowa, which held its nominating contest on Tuesday, was so quick that his record as a U.S. senator and strong conservative views against abortion and gay marriage escaped close attention from his 2012 presidential rivals and the media.His entry into New Hampshire was rocky. College students booed him at New England College over his position against gay marriage and he was forced to explain a remark he...