As Bush campaign ads hit the air criticizing Democrat John Kerry as a flip-flopper, Kennedy tried to paint the president as a reckless, stubborn leader whose Iraq war policies have only fueled the insurgency.
"The president's handling of the war has been a toxic mix of ignorance, arrogance and stubborn ideology," said Kennedy, a Democrat, in a speech to students at George Washington University. "The president's arrogance toward the world community has left our soldiers increasingly isolated and alone."
Meanwhile, he said, the administration continues to insist that the country is safer now because of the war. But Americans "deserve to hear more from our president than happy talk like that," said Kennedy. "The war in Iraq has made the mushroom cloud more likely, not less likely.
Republican Sen. John Cornyn answered back, criticizing Kennedy's nuclear comments.
"Fighting the war on terror globally and fiercely, and treating state sponsors of terror the same as the terrorists themselves, is the only way to succeed and to prevent fighting terrorists on our own shores," Cornyn said.
Separately, on MSNBC's "Hardball With Chris Matthews," Kennedy said that rather than describe their own policies the Republicans have "spent all their resources in distorting and misrepresenting" Kerry's views.
"It's a campaign of anger and insult," Kennedy said. "And the most egregious examples are the examples of Vice President Cheney. When he even goes on to suggest that the al Qaeda wants John Kerry to win, that is the most outrageous charge. It's the most anti-American — it's McCarthyism of the first order."
Kennedy has been criticizing the Bush administration in daily speeches in the Senate, serving as one of the most aggressive boosters of Kerry's presidential campaign.
In his speech Monday, Kennedy said the war in Iraq had created a new breeding ground for terrorists, distracted from efforts to eliminate al Qaeda, alienated America's allies and allowed North Korea and Iran to pursue nuclear weapons.