Leaders continue to wrestle with whether the 2001 attacks should be part of the dialogue on Iraq.

WASHINGTON — The television commercial is grim and gripping: A soldier who lost both legs in an explosion near Fallujah explains why he thinks U.S. forces need to stay in Iraq.

“They attacked us,” he says as the screen turns to an image of the second hijacked airplane heading toward the smoking World Trade Center on Sept. 11, 2001. “And they will again. They won’t stop in Iraq.”

Investigations have shown Iraq did not, in fact, have anything to do with the Sept. 11 attacks. But the ad, part of a $15 million media blitz by an advocacy group allied with the White House, may be the most overt attempt during Congress’ debate over the war to link the attacks with Iraq.

Six years later, the Sept. 11 attacks remain the touchstone of U.S. politics, even as a nation that was united in their aftermath now stands divided on their meaning.

Unlimited Digital Access. $1 for 4 weeks.

While Washington spent Tuesday’s anniversary debating the U.S. involvement in Iraq, it struggled to define the relationship between the war there and the worldwide battle with al-Qaida and other extremists.

During the second day of hearings featuring Gen. David Petraeus and Ambassador Ryan Crocker, the echoes of Sept. 11 reverberated.

Sen. John McCain, R-Ariz., a presidential candidate, got Petraeus to repeat the assertion that Iraq is the “central front in the war on terror.” Sen. Barack Obama, D-Ill., another White House aspirant, complained about the hearing’s timing because it “perpetuates this notion that, somehow, the original decision to go into Iraq was directly related to the attacks on 9/11.”

White House backers, acknowledging Iraqis did not attack the United States on Sept. 11, say the same sorts of people who did are fighting U.S. forces in Iraq.

Some Republicans described the offshoot group al-Qaida in Iraq as the dominant threat on the ground, playing down the sectarian battle for power. Some Democrats called the war a distraction from the hunt for al-Qaida’s Osama bin Laden.

The White House released a five-page document outlining efforts to prevent future attacks and arguing that “we are fighting violent extremists in Iraq and Afghanistan and across the world so that we do not have to fight them on American soil.”

The anniversary comes as U.S. intelligence specialists report that al-Qaida has reconstituted itself in Pakistan, and bin Laden just released news videotapes, in which he made his first appearance in nearly three years.

The failure to capture him bedevils the White House.

The president’s homeland-security adviser, Frances Fragos Townsend, dismissed bin Laden last week as “virtually impotent,” drawing criticism from terrorism analysts. And former Tennessee Sen. Fred Thompson, who just jumped into the Republican race for president, at first dismissed bin Laden’s importance, compared to the broader al-Qaida network, only to retreat and quickly assert that he too wanted to “capture and kill” the al-Qaida leader.

White House press secretary Tony Snow on Tuesday renewed President Bush’s commitment to catching bin Laden. “We’re going to find him,” Snow said. But he added that “the war against terror is not the war against one guy.”

Steve Simon, a former Clinton counterterrorism official, said such comments are not surprising. “What else are they going to say?” he asked. “It’s the sixth anniversary of 9/11 and bin Laden is still out there, probably in Pakistan giving us the finger. At this point, you’ve got to say he doesn’t matter because otherwise it raises important questions.”

Although public support for Bush’s handling of terrorism has fallen, the White House still views al-Qaida as its most successful defense of the Iraq war. After some critics assailed Bush for overstating the connection between bin Laden’s group and al-Qaida in Iraq, the White House quickly arranged a presidential speech to defend and reinforce its assertions.

The reason to emphasize al-Qaida, aides said, is simple. “The average person doesn’t understand why the Sunnis and Shia don’t like each other,” said one senior official who spoke about internal strategy on condition of anonymity. “They don’t know where the Kurds live. … And al-Qaida is something they know. They’re the enemy of the United States.”

The ad campaign, sponsored by a group called Freedom’s Watch, includes four spots in 60 congressional districts, including the Vancouver, Wash., area represented by Democratic Rep. Brian Baird.

Baird triggered outrage among Democrats and many constituents last month by expressing support for Bush’s troop-increase strategy in Iraq.

The commercials urge Congress to stick with the plan.

Former White House press secretary Ari Fleischer, one of the group’s founders, said the ad is not misleading. “Iraqis did not attack us on 9/11,” he agreed. But it does not matter, he added, because the same kind of extremists are fighting U.S. troops in Iraq.

“Nine-eleven absolutely is a bona fide, legitimate reason to remind people what’s at stake,” Fleischer said. “The point is not that Iraq was responsible for 9/11. They’re not. But 9/11 should be a vivid reminder to everyone about how vulnerable our country is and that’s why we need to win in Iraq.”

The question of what relationship the Iraq war has to the broader terrorism fight prompted a tense exchange during Tuesday’s Senate hearing.

Sen. Russell Feingold, D-Wis., a war opponent, suggested the Iraq war has diverted too much attention and resources. “The question we must answer is not whether we are winning or losing in Iraq but whether Iraq is helping or hurting our efforts to defeat al-Qaida,” Feingold said. “That is the lesson of 9/11, and it’s a lesson we must remember today.”

Feingold pressed Crocker to say whether the hunt for radicals in Afghanistan and Pakistan or the campaign in Iraq was more important to defeating al-Qaida.

Crocker would not choose. “Fighting al-Qaida in Pakistan is critically important to us,” he said. “Fighting al-Qaida in Iraq is critically important to us.”

Seattle Times staff contributed to this report.