Obama must walk fine line in Iraq speech.

President Barack Obama must walk a fine line in a speech on Tuesday night as he highlights progress toward winding down the war in Iraq while trying to avoid any perception of a "Mission Accomplished" moment.

The White House says the removal of all but 50,000 U.S. troops and the declaration of the end to the combat phase shows Obama is fulfilling a campaign promise he made in 2008 to pull out of Iraq.

Obama hopes that message will resonate with Americans ahead of the Nov. 2 elections, where his Democrats are struggling to keep their dominance in the U.S. Congress.

The address, scheduled for 8 p.m. EDT/midnight GMT, will be only his second from the Oval Office. Obama also used the high-profile venue in June to discuss his administration's response to the Gulf Coast oil spill.

As Obama prepared to deliver his speech, U.S. Vice President Joe Biden flew into Iraq on Monday to assure Iraqis the United States is not abandoning them.

Biden was to hold talks with Iraqi leaders amid a political deadlock almost six months after an inconclusive election in March over forming the next government.

Obama told NBC News in an interview on Sunday that Iraqis are "going through a political process that is natural in a fledgling democracy" but he added, "we're confident that that will get done."

Obama plans to visit troops at Fort Bliss, Texas, prior to the speech.

In the address, Obama must avoid coming across as too triumphant. To do so could evoke comparisons to President George W. Bush's May 2003 speech aboard an aircraft carrier. In front of a "Mission Accomplished" banner, Bush announced that major combat operations were over, a move that was seen as a huge misstep after violence later exploded.

"You won't hear those words coming from us," White House spokesman Robert Gibbs said of the Mission Accomplished slogan. "Obviously tomorrow marks a change in our mission. It marks a milestone that we have achieved in removing our combat troops."

"That is not to say that violence is going to end tomorrow," Gibbs added.

More than 4,400 U.S. soldiers have died in Iraq since the U.S.-led invasion in 2003 to topple Saddam Hussein.

Obama, who opposed the Iraq war, rode a wave antiwar sentiment that boosted his support within his Democratic Party during the 2008 campaign.

When he took office in January 2009, the U.S. troop presence in Iraq was 140,000 troops and it reached a high of 176,000 under the surge ordered by Bush.

The roughly 50,000 U.S. soldiers still in Iraq are moving into an advisory role in which they will train and support Iraq's army and police.

The effective change on the ground will not be huge because the U.S. military has already been switching the focus toward training and support over the past year. Obama has promised to pull all U.S. troops out of Iraq by the end of 2011.

Ahead of the speech, Republicans criticized Obama for what they say is a failure to acknowledge the success of Bush's troop surge in bringing down violence in Iraq. Obama had opposed the 2007 troop increase.

Gibbs said additional troops contributed to the reduction in violence but there were a "host of factors" that also played a role, such as the "Sunni awakening" movement in which Sunni tribesmen and former insurgents decided to fight al Qaeda.

Obama plans to call Bush before the speech, Gibbs said.

One of Obama's aims is to ease growing anxiety among liberals in his party about the war in Afghanistan, where he has increased U.S. troop levels.

He has set July 2011 as the date for a beginning of a drawdown of U.S. forces in Afghanistan and he hopes the example of Iraq will reassure his Democratic supporters that he can keep his word.

Also looming in the background of Obama's speech are growing worries about the U.S. economy.

The Iraq speech and a Middle East peace summit he is hosting on Wednesday and Thursday mark a heavy emphasis on foreign policy this week. But a raft of gloomy economic data has dominated Americans' attention, which could potentially steal some of the thunder from the Iraq speech.

Obama, who visited wounded troops on Monday at Walter Reed Army Medical Center in Washington, will use the Fort Bliss trip to pay tribute to the troops who have served in Iraq.

More than 7,000 troops from Iraq have returned to Fort Bliss over the last six months, including members of the 1st Brigade Combat Team who came back in August and were among the most recent wave of troops to leave, according to the White House.