ATLANTA (AP) — Hardly the start he'd hoped for, Newt Gingrich's first week as a presidential candidate has been riddled with missteps that have angered many of his fellow Republicans and exposed campaign vulnerabilities.

The former U.S. House speaker disparaged House Republicans' Medicare proposal as "right-wing social engineering" and was all but forced to apologize after the conservative outcry. He tied himself in knots when he defended part of the Democrats' health care law — which he says he opposes. And he refused to explain a $500,000 debt he once owed to the upscale Tiffany's jewelry store though railing against President Barack Obama for what he calls excessive federal spending.

"He has severely damaged his campaign and his credibility," said Debbie Dooley of Duluth, Ga., a national coordinator for the Tea Party Patriots who contended that Gingrich made things worse when he tried to explain his health care stance favoring a requirement that Americans have coverage. "If he continues with that position, for the most conservative tea party Republicans … it's over," she said.