Senator Harry Reid of Nevada, the majority leader, said that “the president’s claim that the war in Iraq is protecting us from Al Qaeda is as misguided and dangerous as the conclusions that drove us to Iraq in the first place.”

“Despite what the president would like us to believe,” he added, “it has been established that Al Qaeda had no active cells in Iraq when we invaded, and we have long known that we were not attacked from Iraq on 9/11. Saying otherwise does not make it so.”

Still, judging by recent opinion polls, the president has had some recent success in making a case to voters for continuing the war in Iraq. He has insisted both that success is possible and that failure would be catastrophic, in part because Al Qaeda in Iraq might then turn its attentions elsewhere.

Earlier today, the White House spokesman, Tony Snow, was asked why Mr. Bush felt the need at this point to insist that the two Al Qaeda groups were closely connected.

“I think, when somebody tries to argue that Al Qaeda in Iraq is not a key part of the problem, it creates a basis of saying, well, you need to go someplace else,” he said.

Mr. Bush emphasized in his remarks that Al Qaeda in Iraq’s top leaders include people from Jordan, Saudi Arabia, Tunisia and Turkey, and said that American forces had recently unmasked an effort by the group to pass off an Iraqi actor, using the surname al-Baghdadi, as its leader to give it a more Iraqi image.

Mr. Bush said that after the United States-led invasion of Iraq in 2003, Mr. Zarqawi “was able to expand dramatically the size, scope and lethality of his operation,” and that he swore formal allegiance to Mr. bin Laden the following year.