WASHINGTON (AP) — Seeking war power authority for three years, President Barack Obama is setting up the prospect that his successor will become the third American president in a row overseeing U.S. military forces grappling with turmoil in the Middle East.

Passing on an active military mission in the region would be an unexpected and unwanted legacy for Obama, a president who once appeared poised to fulfill his campaign pledge to end U.S.-led conflicts in the region.

"It's conceivable that the mission is completed earlier," Obama said Wednesday as he urged Congress to pass a force authorization against the Islamic State group that would extend into 2018. "It's conceivable that after deliberation, debate and evaluation, that there are additional tasks to be carried out in this area."

"The people's representatives, with a new president, should be able to have that discussion," he added.

The president has long said the campaign against the Islamic State militants would be lengthy, suggesting it could extend beyond his presidency. But his authorization request to Congress makes that implication a reality and injects a complex foreign policy matter into the early stages of the 2016 presidential campaign.

Under Obama's proposal, the use of military force against Islamic State fighters would be authorized for three years, not limited by national borders. The fight could be extended to any "closely related successor entity" to the Islamic State extremists, but the measure does not authorize large-scale ground operations.

The very act of Obama asking Congress to authorize military action in the volatile Middle East marks an extraordinary moment in his presidency. Congress hasn't approved a presidential request for military action since 2002, when George W. Bush asked lawmakers to give him authority to set the Iraq war in motion.

Obama ended that long, expensive and unpopular war in 2011. But he turned to that same 2002 authority last year, when he sought a legal justification for sending a few thousand troops back to Iraq to protect American interests and work with local forces fighting the violent and fast-growing Islamic State group.

By late summer, the U.S. was launching airstrikes against the militants in Iraq, as well as Syria.

As a presidential candidate, Obama said he would have voted against the authorization Bush sought in 2002, a position that helped him distinguish himself from Democratic rival Hillary Rodham Clinton, who voted for the measure while in the Senate. Clinton later said she regretted that vote.

Obama's proposed legislation would repeal the 2002 Bush authorization. He has said that while he does not believe he legally needs new authority for the military campaign already underway, having Congress pass a new measure would send an important message about American unity and more accurately define the current mission.

Clinton, who is expected to seek the Democratic nomination is 2016, has not weighed in on the draft Obama sent Congress Wednesday, nor did most of the likely Republican candidates.

Among the potential GOP candidates who did comment was Florida Sen. Marco Rubio, who said it was "good news" that Obama submitted the request to Congress but faulted the president for putting limits on the tactics the military could use to fight the Islamic State group. And Rick Santorum, the former Pennsylvania senator who is weighing a second White House run, said the president's proposal puts the nation in an "untenable position."

"The next president needs to be able to have all the tools at their disposal to not just conduct military operations, but win this war," he said in a statement.

Whether Obama's request will be in force when the next president takes office is a huge open question. With the House set to hold hearings on the measure Thursday, there were few, if any, lawmakers in either party who said they outright supported the draft legislation.

While Republicans criticize the legislation for being too limiting, some Democrats fear the wording is too vague and leaves too much room for the conflict to expand. The wide gap between the parties' criticisms could make it difficult for the White House to find a way to bridge the differences.

For the president, the outcome of the congressional debate could be as central to his legacy as the outcome of the fight on the ground in Iraq and Syria. That reality did not appear to be lost on Obama as he appealed for congressional support for a strategy he insists will succeed.

Turning to unusually blunt language for a president who tends to prefer context-filled soliloquies to soundbites, Obama declared: "ISIL is going to lose."

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EDITOR'S NOTE — Julie Pace has covered the White House for The Associated Press since 2009.

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Follow Julie Pace on Twitter at http://twitter.com/jpaceDC