Here’s how I imagine the scene when President Bush appears in Madison Square Garden at the Republican National Convention.

The president will address the crowd from a circular stage, but above him will float the shadows of three bearded men in turbans. Two will be Iraqis: Grand Ayatollah Ali al-Husseini al-Sistani, the preeminent Shiite cleric, and his radical challenger, Muqtada al-Sadr. Behind them hovers the gaunt figure of Osama bin Laden.

These three men may not be physically present at the convention, but they will play a key role in whether Bush wins a second term.

For the first time since the Vietnam era, national security is the central issue in a presidential election, according to a poll released this month by the Pew Research Center. Four out of 10 respondents said war, terrorism and foreign policy were the key questions facing the nation. Only one quarter put the economy at the top of the list.

With 140,000 U.S. troops in Iraq and no exit strategy in view, the fate of the self-described “war president” may depend on how the Iraq war plays out in the coming weeks. Fifty-two percent of Americans dislike the way Bush is handling Iraq, and 58 percent say he has no clear plan for bringing the situation to a successful conclusion, according to Pew.

Last week’s bloody events in the Iraqi holy city of Najaf offer further grounds for questioning the presidential performance on Iraq.

Here’s a brief summary of the Najaf drama:

U.S. Marines tried to crush the radical al-Sadr, whose armed forces have been battling coalition troops on and off for months. Al-Sadr’s Mahdi Army had holed up in and around Shiite Islam’s holiest shrine, the Imam Ali mosque in Najaf.

The Marines, who leveled much of downtown Najaf, couldn’t defeat al-Sadr’s forces without damaging the mosque and thus turning most Shiite Muslims against the United States. Interim Iraqi Prime Minister Ayad Allawi had no troops capable of doing the job.

Enter the aging Sistani, whose status had been challenged by the more aggressive and semiliterate al-Sadr. Sistani, a virtual recluse, had left for an angioplasty in London rather than stay around as Marines pounded central Najaf. But suddenly, without consulting the Americans or Allawi, he flew back to Iraq and brokered a face-saving deal to end the Najaf siege.

The ayatollah got the credit for saving the city (after the Marines had weakened his adversary). He made Allawi’s secular government look hapless. He called for U.S. forces to withdraw from Najaf, even as al-Sadr and his men are supposed to quit the mosque and go free; presumably they will reorganize to fight another day. This is not a victory for the Marines, nor for the Iraqi government.

The upshot: Sistani is, for now, the most powerful figure in Iraq. The good news: Unlike al-Sadr, he doesn’t advocate a Khomeini-style Islamic state where clerics rule. Sistani wants elections so the majority Shiites will finally run the country. He does, however, believe that politicians and U.S. forces should heed the fatwas of ayatollahs.

The bad news: Our president’s Iraq venture depends on the whims of a 73-year-old Shiite cleric. Should Sistani sour on the U.S. military presence, he can turn millions of followers out into the streets. Should Sistani’s heart fail, the most powerful Shiite figure in Iraq would be young al-Sadr.

The Najaf episode is a reminder of how little the president knew about Iraq before the war, or about the growing strength of religion inside the country. Remember when he told us he would make Iraq into a democratic role model for the Middle East? We will probably hear this refrain again in New York.

Bush acknowledged last week for the first time that he made a “miscalculation of what the conditions would be” in postwar Iraq. But you aren’t likely to hear much discussion in Madison Square Garden about what went wrong.

You won’t hear how continuing instability and unemployment in Iraq send recruits into al-Sadr’s fold. Nor will you hear how scenes of Iraqi violence on Arab satellite TV increase the recruitment pool for bin Laden.

I hope you’ll hear the president say that he has sent urgent aid to Najaf for rebuilding. Otherwise, the local Shiites might start comparing the destruction of their city to the devastation wreaked on Najaf in 1991 by Saddam Hussein.

Just after the Gulf War ended they rebelled against Saddam, in response to a call by the first President Bush. He then let Saddam crush the rebellion. I was there in April 1991 and saw the gruesome results. The Shiite religious establishment still blames the United States for the 1991 disaster.

This time Najaf was crushed by its professed liberators. Though most Najafis despise al-Sadr, they will blame Americans for wrecking their city. This is the kind of confusion into which President Bush unwittingly led us. There’s no sign he knows how to lead us out.

Trudy Rubin is a columnist for the Philadelphia Inquirer.