WASHINGTON -- U.S. President Barack Obama is asking Congress to do something it hasn’t done in more than 12 years: vote to authorize war. It could be one of the most difficult votes taken in Congress during Obama’s tenure, rife with political calculations and the difficulty of convincing a bipartisan majority of a deeply divided body to back a bill.

The administration already began to lay the groundwork to get enough members of Congress behind an eventual bill. But a path remains difficult as the competing political interests -- Republicans who don’t want to do Obama any favors and Democrats who don’t want another war -- try to find a compromise through a series of hearings and debates.

Congress hasn’t actually declared war since World War II. Instead, conflicts in the intervening years have been blessed by legislation known as Authorization of Use of Military Force, or AUMF. And Congress hasn’t voted on such a bill since Obama took office. He’s conducted the wars in Iraq and Afghanistan under the authorizations passed by Congress in 2001 and 2002. He has argued he could find the legal basis to fight the Islamic State group in Syria under those authorizations. But he’s asking Congress now to pass another authorization. This one will likely include broad ability to engage in different geographic regions, but unlike the previous AUMF, it will include a three-year expiration date.

A significant number of Democrats and Republicans are going to be needed in both chambers for AUMF to pass. In contrast with other pieces of controversial legislation, it’s unlikely either party will be able to produce the bulk of the votes. And that means balancing a lot of competing interests.

For Republicans, it’s not about war, but about who will be conducting the war. There is the reflexive anti-Obama element in play for many Republicans, especially the right flank of the GOP. There’s a core group who would be hard-pressed to approve anything that Obama requested from Congress. 

The political struggle runs much deeper for Democrats. The left holds much stronger anti-war sentiments.

Democrats, especially those who see themselves as future presidential candidates, remember the trouble the Iraq War vote caused members of their party. Hillary Rodham Clinton, John Kerry and John Edwards all faced criticism for supporting the Iraq War when they ran for president. Clinton is still taking heat for her 2002 vote. Kerry was ridiculed for his decision to vote for the authorization, but then against its funding -- a move that George W. Bush’s campaign used to depict him as a flip-flopper.

The White House appears to be taking deliberate steps to mitigate the political backlash. White House staffers have been sent to the Hill to brief members of both parties. They reached out to key members of the GOP -- and not just Sen. John McCain of Arizona. The administration provided language, but opted for an outline instead of trying to write the legislation. That will allow Obama to be flexible as members of Congress make adjustments. It’s distinctive from the process in 2013 when the president asked Congress for authorization to strike in Syria as rebels fought the nation’s government. That request landed with a thud, and Obama couldn’t even get Congress to hold a vote.

The circumstances have changed dramatically since then. When Obama made his last request, hardly anyone was talking about the militant group formerly known as either ISIL or ISIS. Since then, the terrorist organization has become a household name. The executions of hostages -- including a Jordanian pilot who was burned alive -- have generated loathing of the extremist group. 

The recent announcement of the killing of American Kayla Mueller, who was being held captive by the Islamic State group, is likely to increase support for authorizing strikes against it, perhaps making it easier politically to vote for the authorization request than to oppose it. Mueller was the first Western woman killed by the militant group.

“Kayla’s death adds to it,” Rep. Raul Grijalva, D-Ariz., said. “The circumstances and visuals have changed for the American people and Congress.”

In a speech Wednesday afternoon explaining his AUMF request, Obama called for a thoughtful and dignified debate on the issue. And so far there has not been a partisan backlash. While members on both sides criticized elements of the outline, not one member ruled out entirely the possibility of voting for an amended version. House of Representatives Speaker John Boehner of Ohio was cautious, expressing some concerns but repeatedly emphasizing that it was the beginning of a longer process.

“I’m not going to get into any of the specifics,” Boehner said. “This is the beginning of a legislative process, not the end.”

Conservatives responded to Obama’s outline by saying they would review it and make a decision -- a much different response than they’ve had to almost anything else the president has done. “You’re at risk if you hand this president a blank check,” Rep. Tim Huelskamp, R-Kan. said. But he didn’t rule out supporting the bill. “I want to know what the cost is in terms of dollars and in terms of lives. People are tired of war in my district.”

Liberals are holding their fire, too. “I think there is a marked difference between us remaking a commitment to a land war in which we lead, which hasn’t proven to be the best strategy in two other places, Afghanistan and Iraq, versus being the supplemental support internationally, being the key supplemental support,” Grijalva said. “I don’t think we can be the main policemen in that conflict.”

It’s a far cry from how Obama handled the rollout of his immigration executive orders last year. There was no attempt to make nice with Congress. No effort to give opponents a preview and reduce the backlash. Obama made the announcement and then dared Republicans to fight him.

This time, he’s going to give them them a chance to weigh in. The legislation will be crafted as a result of hearings in committees and likely undergo a good deal of input from both parties.

“I think what’s going to happen, the plan is that this will be highly debated in at least one committee, and maybe two, and lots of members will have ideas, and we recognize that people need to be heard from,” said House Rules Committee Chairman Pete Sessions of Texas. “My hope is that there is vigorous debate, and I think there will be.”