Sens. Hillary Clinton, D-N.Y., and Barack Obama, D-Ill., have been at odds ever since Obama said at a debate in South Carolina that if elected he would meet with leaders of hostile nations during his first year in office.

Clinton advisers quickly cast his answer as a rookie mistake and Clinton referred to the junior senator from Illinois as "irresponsible and, frankly, naïve" during an interview in Davenport, Iowa, The Washington Post (NYSE:WPO) reported Friday.

Obama called Clinton's wait-and-see position "Bush-Cheney lite," prompting Clinton to ask on CNN "Whatever has happened to the politics of hope?"

By Thursday night senior aides to the two were quarreling on television.

The newspaper said the tussle could be a turning point in the Democratic race framing the differences between Clinton and Obama as her experience versus his freshness.