US: Rival candidates have turned up the heat on front-runner Mr Howard Dean in the latest Democratic debate in the race for the White House in 2004.
Meanwhile, the first Bush campaign ad, which questions the Democrats' commitment to the war on terrorism, has backfired with the revelation that officials doctored the president's voice to improve his diction.
Mr Dean came under sustained criticism from Sen John Kerry and Congressman Richard Gephardt for cuts in services he made while governor of Vermont.
The most confrontational moment in the debate, held in Iowa where a Democratic caucus will take place in January, came when Sen Kerry, taking part by video link from Washington, repeatedly demanded to know why Mr Dean would not promise that, as president, he would not slow the growth of Medicare spending. "Are you going to slow the rate of growth - yes or no?" asked Mr Kerry. Mr Dean replied: "We're going to do what we have to do to make sure that Medicare lasts."
A focus group of some 25 Democratic voters assembled by MSNBC television voted Mr Dean the winner of the exchanges because he kept his cool under fire.
The debate of the nine candidates - minus Sen Joseph Lieberman who is not contesting Iowa - was marked by an anti-war outburst from retired Gen Wesley Clark.
Gen Clark has been criticised by anti-war Democrats for an early interview in which he said he would probably have voted for the Congress resolution authorising military action against Iraq. "I bobbled the question on the first day of the campaign," he said. "The real issue in front of us is that this president misled the American people and the Congress into war. It's wrong."
The doctoring of Mr Bush's voice in the Republican campaign ad was first noticed by aides to Mr Dean.
Mr Bush was shown telling Congress in his State of the Union address in January: "It would take one vial, one canister, one crate slipped into this country to bring a day of horror like none we have ever known."
However, in the address he had stumbled between the words "one" and "vial" and pronounced "vial" as "wial". The word is correctly pronounced in the commercial.
Republican officials said the line was "cut and pasted" from other parts of the speech and that Mr Bush was not asked to re-record.
"Audio cutting and pasting is Bush-speak for them having doctored their own ad," Mr Jim Mulhall of the Democratic National Committee told the New York Times.
The advertisement has infuriated Democrats because it attacks their commitment to the war on terrorism.