Senator John Kerry charged late Thursday that President George W. Bush committed "a colossal error" by invading Iraq, as they clashed in a high-stakes debate that may decide their battle for the White House.
As tens of millions of Americans watched the televised confrontation, Bush countered that Kerry was undermining US credibility in the war on terrorism with "mixed messages" about whether toppling Saddam Hussein was worth the cost.
"What message does that send our troops? What message does that send to our allies? What message does that send the Iraqis?" the Republican incumbent asked. "The world is better off without Saddam Hussein."
Iraq and national security dominated as the two candidates battled over how to stabilise that war-torn country, where more than 1,000 US soldiers have died amid deadly chaos that shows no sign of ebbing.
Kerry went into the debate needing a strong performance and some instant polls straight after said he had beaten the president. A Gallup poll for CNN gave Kerry a 46 percent to 37 percent win over the president.
Leading US dailies on Friday agreed that the debate was a tie. "If Americans who tuned into last night's presidential debate were waiting for one of the candidates to catch the other in a fatal error, or leave him stammering, the event was obviously a draw," wrote The New York Times.
Kerry threw the first punch in the political prize-fight by confidently declaring "I can do a better job" on Iraq and on averting another terrorist attack like the September 11, 2001 strikes.
He also charged Bush unnecessarily diverted resources from the hunt for Osama bin Laden to the war in Iraq, saying: "This president has made, I regret to say, a colossal error of judgement. And judgement is what we look for in the president."
"The world is better off without Saddam Hussein," said the president, who painted his rival as fickle on crucial national security issues, noting he voted to authorise the Iraq war in 2002 but against war funding in 2003.
"We're not going to achieve our objective if we send mixed signals to our troops, our friends, the Iraqi citizens," said Bush. "You cannot lead if you send mixed messages."
"I've had one position, one consistent position, that Saddam Hussein was a threat. There was a right way to disarm him and a wrong way. And the president chose the wrong way," countered the Massachusetts senator.
Kerry has accused Bush of fracturing alliances and damaging US global standing in the rush to war; Bush has charged Kerry is more worried about world-wide popularity than protecting the United States.
Before the confrontation, the Republican and Democratic rivals shook hands and exchanged tense smiles before taking cover behind matching lecterns.
Kerry, a four-term senator, has trailed in polls that indicate that undecided voters may be open to a change of president, but have yet to warm to him.
Bush hoped to build on a five-to-eight point edge in national polls and leads in many of the battleground states expected to decide one of the most hard-fought elections in recent US history.
Kerry's backers were convinced their man had done enough to jolt the White House race back to life, and claimed Bush looked edgy and defensive.
Outspoken Democratic National Committee Chairman Terry Mcauliffe claimed Kerry came out as the statesman of the pair, while Bush looked like "an ostrich who has his head in the sand."
Republican spin masters claimed the president's opponent had once again been exposed as indecisive.
"This debate showed that John Kerry is once again willing to say almost anything that suits his political moment," said top Bush advisor Karen Hughes.
The Los Angeles Times presented its readers with what it believes is the real conundrum: "Kerry won Thursday night's debate on foreign policy by a comfortable margin, but Americans may yet decide that President Bush is better able to clean up the mess he created in Iraq." The first of the three debates went ahead amid mounting chaos in Iraq. At least 49 people were killed there, dozens of them children, in three nearly simultaneous car bomb attacks Thursday.
US and Iraqi forces poured into central Samarra early Friday to seize the trouble-spot's government building and police stations in an attempt to beat back the insurgency, the US military said.
"This president, I don't know if he sees what's really happened on there. But it's getting worse by the day," said Kerry.
"If we lose our will, we lose. But if we remain strong and resolute, we will defeat this enemy," said Bush.
The candidates' different styles were on display early. Kerry sought to back up policy proposals with statistics and details while Bush countered with broad principles he said fuelled his outlook.
Amid signs of slipping US public support for his policy towards Iraq, Bush sounded defensive, and frequently shot annoyed glances at Kerry, who in turn frequently looked down at his notes during the president's answers.
The two clashed on approaches to the North Korean nuclear crisis - Bush warning against Kerry's call for bilateral talks - and to Iran's moves to develop a nuclear programme.
But both agreed that the most serious threat to US national security was the possibility that terrorists like Osama bin Laden's al Qaeda network might get their hands on nuclear materials.
And Kerry and Bush called the violence sweeping through Sudan's troubled Darfur region "genocide" while saying they opposed sending US troops there.
Kerry and Bush will have a second debate, on October 8 in St. Louis, Missouri, and finish with a session on domestic policy October 13 in Tempe, Arizona.