Obama responded that "my objection to the war in Iraq was not simply a speech".
The debate was the last the pair held before March 4, when Rhode Island and Vermont will join Ohio and Texas to hold primaries.
Obama has won the last 11 primaries or caucuses, leading Clinton in many national polls and edging slightly ahead in most news organizations' counts of delegates to the Democratic National Convention.
The Clinton campaign team has consistently acknowledged that it must do well in Ohio and Texas, where she has enjoyed a wide lead in public opinion polls, to have a realistic shot at taking the nomination, but the latest surveys ahead of the debate were not promising.
Obama has narrowed the gap with Clinton to 6 percentage points in an Ohio poll released Tuesday.
He trailed by 9 points in the same poll last week and 17 points two weeks ago in a state that the Clinton campaign has long seen as a "firewall" against Obama's surging popularity.
Obama's gains were even more dramatic in Texas, where he has overtaken Clinton in the past week, according to a Texas poll released Tuesday.
(Xinhua News Agency February 27, 2008)
