President Barack Obama is accusing Republican Mitt Romney of caving under pressure from Rush Limbaugh for saying that requiring all Americans to buy health insurance amounts to a tax.

Obama says in an interview with NBC affiliate WLWT in Cincinnati that Romney supported the individual mandate as Massachusetts governor but "has suddenly reversed himself." Obama says it raises questions over whether Romney is abandoning a principal after "getting pressure for two days from Rush Limbaugh" or other critics.

Romney said Wednesday the Supreme Court ruled the requirement to buy health insurance was a tax, amounting to a shift in position. A top Romney adviser said previously that Romney viewed the mandate as a penalty, a fee or a fine - not a tax.

Obama says "principles matter" as president.