President Barack Obama told congressional leaders on Tuesday he has the authority to carry out his planned strategy against ISIS fighters in Iraq and Syria without authorization from legislators, but he asked for their support to show the nation was united.
Obama "reiterated his belief that the nation is stronger and our efforts more effective when the President and Congress work together to combat a national security threat" like the Sunni jihadists who call themselves the Islamic State, a White House statement said.
"The President told the leaders that he would welcome action by the Congress that would aid the overall effort and demonstrate to the world that the United States is united in defeating the threat," it added.
Earlier, two senior legislators -- one from each party -- told CNN's Dana Bash that a congressional vote on military action against the jihadists was unlikely despite calls for one by many of their colleagues.
While some in Congress want to vote on the matter, taking up such a volatile issue as military action weeks before the November elections may be politically dangerous.
Others in Congress argued the President already has the authority he needs to expand attacks on ISIS under war powers granted more than a decade ago to go after al Qaeda.
Obama has been criticized by conservatives and some Democrats for what they call a timid response so far to the threat by ISIS fighters who emerged from Syria to rampage through northern Iraq.
The President authorized airstrikes on ISIS targets in Iraq earlier this year, but he now faces pressure to expand the campaign to go after the extremists in Syria.
Obama and his top aides call such a military step one part of a broader strategy against ISIS that includes establishing a stable representative government in Iraq, forming an international coalition including Middle East countries to combat the extremists and increasing military aid to moderate opposition groups in Syria fighting ISIS and the government of President Bashar al-Assad.
The top Republicans and Democrats from the House and Senate -- House Speaker John Boehner of Ohio and Senate Republican leader Mitch McConnell of Kentucky, along with Senate Majority Leader Harry Reid of Nevada and House Democratic leader Nancy Pelosi of California -- got the first glimpse of Obama's plan to "degrade and defeat" ISIS at a White House meeting on Tuesday.
Afterward, Boehner said in a statement he would support Obama if the President deployed the U.S. military to help train and advise Iraq forces and assist with targeting ISIS leadership.
"I think we have to take them out," Democratic Sen. Ben Cardin of Maryland told CNN on Tuesday, in reference to targeting ISIS leaders.
Administration officials also planned to brief all legislators this week on the the threat from the extremists who call themselves the Islamic State, while Secretary of State John Kerry left Tuesday to push Sunni leaders in Jordan and Saudi Arabia to join the United States and its allies in combating ISIS.
Next week, Kerry and Defense Secretary Chuck Hagel will appear at congressional hearings to discuss the President's ISIS strategy, the White House said.
A year ago, Obama failed to secure congressional support for airstrikes inside Syria after international observers concluded al-Assad used chemical weapons on civilians.
Obama launched the current air campaign against ISIS in Iraq, which has included more than 100 strikes against the militants, without specific approval from Congress beyond the President's power to protect American interests abroad and help alleviate humanitarian situations.
White House lawyers must determine whether a plan to go after ISIS further, which could include airstrikes on targets inside Syria, would require a vote in Congress.
Polls have long showed Americans tired of war after lengthy engagements in Iraq and Afghanistan, though a CNN survey released Monday indicated 76 percent supported additional airstrikes against ISIS. More than seven in 10 said Obama should ask Congress for approval, and eight in 10 said Congress should grant it.
"If this is going to be a prolonged fight against ISIS, it seems to me that there is no way to avoid coming to the Congress for an authorization for the use of military force, which comes before the Senate Foreign Relations Committee," said Sen. Robert Menendez of New Jersey, the Democratic chairman of that panel.
Republican Rep. Peter King of New York, however, told CNN on Tuesday that Obama should act first and get the approval from Congress afterward.
"This is so imminent, this is so critical, I want the President to take the action and then Congress should pass legislation supporting what the President does," King said. "I don't want him to wait until Congress acts because I don't have full faith in Congress myself, to be honest with you."
The White House said it's continuing to seek a "buy-in" from Congress on any plan to defeat ISIS, though officials say that doesn't necessarily mean a vote on military action.