President Bush's decision to send 21,500 more troops to Iraq and to redouble other US diplomatic and economic efforts there could prove a fateful pivot point of both his presidency and US involvement in the Middle East.
The move puts Mr. Bush on a collision course with Democrats in Congress who believe that it is time to begin planning a reduction in US force levels, not an increase. Not since the Vietnam War has Washington seen the executive and legislative branches of government fight openly over the direction of an ongoing conflict.
It also amounts to something of a gamble on the Iraqis themselves. Administration officials were careful to describe their new way forward as a response to requests from the Iraqi government, and insisted that Iraqi units, not US ones, would take the lead in the coming campaign to quell rampant sectarian violence.
At the same time, administration officials insisted that Iraqi leaders will have to meet performance benchmarks if they want continued US support. Some analysts see this as a possible escape hatch for the US if the situation continues to deteriorate.
"America will now only surge [troops] if Nouri al-Maliki's government makes a deal to share oil wealth and reintegrate former Baathists, things it has shown no willingness to do," wrote Peter Beinart, a senior fellow for US foreign policy at the Council on Foreign Relations, in an analysis of the president's address.
Bush's 20-minute address to the nation Wednesday night was notable for its sober tone and admission that things are not going well in Iraq.
While Iraq's 2005 elections gave reason for hope, said Bush, 2006 saw those hopes dashed.
"The violence in Iraq, particularly in Baghdad, overwhelmed the political gains the Iraqis had made," he said.
Eighty percent of the violence occurs within a 30-mile radius of Baghdad, Bush noted. He said efforts to pacify the city had failed for two reasons: There were not enough Iraqi and American troops to secure neighborhoods that had been cleared of terrorists and insurgents, and there were too many political restrictions on the troops that were there.
Now the Iraqi government has promised to commit 18 Army and national police brigades to help control Baghdad, said the US president. These will be augmented by five US brigades deployed to Iraq.
"These troops will work alongside Iraqi units and be embedded in their formations," said Bush.
The Iraqi government has promised it will not prevent any moves for political reasons, said a senior administration official who briefed reporters on the new plan. In other words, even if units want to raid Sadr City, a Baghdad neighborhood that is the redoubt of Moqtada al-Sadr's powerful Shiite militia, they can.
US forces will be embedded with Iraqis down to the company level, said the senior official. And the US may be able to tell soon how reliable a partner in this effort the Maliki government will be. The Iraqis have promised to get one new brigade into Baghdad by the first of February, and two more by Feb. 15.
"People are going to be able to see pretty quickly that the Iraqis are or are not stepping up," said the administration official.
The Iraqi government has also pledged to pass legislation dividing the country's oil wealth evenly among its citizens, according to US officials, and to spend $10 billion of its own cash on reconstruction.
Nor is the US effort to be purely military, according to Bush. US civilians and military commanders operating in Iraq will get more flexibility to disperse economic aid. The number of US provincial reconstruction teams will be doubled. Secretary of State Condoleezza Rice will soon appoint a new US reconstruction coordinator in Baghdad.
The US must succeed, insisted Bush, because the consequences of failure are grim.
"Radical Islamic extremists would grow in strength and gain new recruits," said the president. "They would be in a better position to topple moderate governments, create chaos in the region, and use oil revenues to fund their ambitions."
Some key figures in Congress applauded the president's plan.
"The most important thing is he laid out a new strategy instead of just increasing troops," said Sen. John McCain (R) of Arizona.
But Bush's redoubled effort in an increasingly unpopular war also makes some Republicans uneasy and many Democrats unhappy.
"Escalation of this war is not the change the American people called for in the last election," said Sen. Richard Durbin (D) of Illinois, the new Senate majority whip.
It is possible that even 20,000 more US troops will not be enough, according to some military experts. And, in general, Bush's address seemed to ignore the fact that the Iraqi government and Iraqi security forces are themselves riven by sectarian differences.
Even some who believe the changes ordered by the US administration are generally sensible worry that they are now too little, too late.
"The president is correct to point out that failure will be a disaster for Iraq, the Middle East more generally, and the United States itself," said Gideon Rose, managing editor of the journal Foreign Affairs. "One can only wish that his administration had taken this concept to heart from the beginning and planned and acted accordingly."
• Staff writer Gail Russell Chaddock contributed to this report.