Kerry repeatedly accused Bush of rushing to war in Iraq and disdaining the diplomatic route to neutralizing Iraqi President Saddam Hussein.
Bush repeatedly reiterated his belief that Iraq is the central front in the war against international terrorism, and that an American president cannot waver or rely on dissenting allies in a time of war.
Throughout the debate, Bush accused Kerry of changing his position on the war: first voting in the Senate to authorize the use of force against Iraq, then calling it the wrong war in the wrong place at the wrong time.
Kerry responded that his Senate vote was to authorize force only if necessary, and only after all diplomatic efforts had been exhausted. If anything, the senator said, it is Bush who has changed his position.
"He [Bush] gave a speech in which he said, 'We will plan carefully, we will proceed cautiously, we will not make war inevitable, we will go with our allies.' He didn't do any of those things," Kerry said of Bush.
Kerry said Bush rushed into war, scorning the counsel of America's traditional allies, and that the president still refuses to ask them to share the burden. Instead, he said, U.S. forces are suffering 90 percent of the casualties in Iraq, and U.S. taxpayers are burdened with 90 percent of the cost.
Bush responded that a Kerry presidency, with what he called its muddled view of the war, would demoralize American troops in Iraq, and would not persuade more nations to share in the task of pacifying the country.
"He [Kerry] says the cornerstone of his plan to succeed in Iraq is to call upon nations to serve," Bush said. "So what's the message going to be? Please join us in Iraq for a grand diversion? Join us for a war that is the wrong war at the wrong place at the wrong time?"
Bush and Kerry also differed over Russia. The moderator asked Bush if he had misjudged Russian President Vladimir Putin, who has a record of limiting democratic reform. Bush has publicly declared Putin his friend, and once said he looked into Putin's soul and found him trustworthy.
Last night, Bush called Putin a strong ally in the war against international terrorism, but he expressed concern that the Russian leader appears not to believe in what he called the "checks and balances" of democracy.
Still, Bush said, it is important that the two men's relationship remains cordial so they can differ constructively.
"I've told him [Putin] my opinion. I look forward to discussing it more with him as time goes on," Bush said. "Russia's a country in transition. Vladimir is going to have to make some hard choices, and I think it's very important for the American president as well as other Western leaders to remind him of the great benefits of democracy, that democracy will best help the people realize their hopes and aspirations and dreams."
Kerry called for firmer treatment, and rejected Putin's assertion that his tightening of political control is merely a response to Chechen terror.
"I regret what's happened [in Russia] in these past months, and I think it goes beyond just the response to terror," Kerry said. "Mr. Putin now controls all the television stations [in Russia], his political opposition is being put in jail. And I think it's very important for the United States, obviously, to have a working relationship [with Russia] that is good. This is a very important country to us, and we want a partnership, but we always have to stand up for democracy."
Kerry and Bush also differed over North Korea. Kerry said that as president, he would resume direct, bilateral talks with Pyongyang. He said Bush's rejection of direct talks has led to the current North Korean nuclear weapons crisis.
Bush countered that multilateral talks involving Russia, China, Japan, and South Korea -- as well as the United States and North Korea -- are important because they involve nations that are influential in the region. He said that resuming direct, bilateral talks would prompt North Korea to abandon the multilateral negotiations.
Bush said he hoped similar negotiations could help resolve questions about Iran's nuclear aspirations. Kerry contended that any success in those talks would be attributable to Britain, France, and Germany. He said the United States largely ignored the talks until recently.
The two men will meet again on 8 October in the central city of St. Louis. Their final debate will be held 13 October in the southwestern state of Arizona. Vice President Dick Cheney and his challenger, Senator John Edwards (Democrat, North Carolina), will debate 5 October in the central industrial city of Cleveland.