President Obama's language on war has evolved throughout his time in office. From his Nobel Peace Prize speech in 2009 to his remarks on the Islamic State, here are his remarks over the past six years. (Nicki DeMarco/The Washington Post)

For more than two years, President Obama and his top aides argued that providing U.S. arms and equipment to the moderate Syrian rebels was an undesirable, high-risk approach with the potential to further destabilize an already chaotic region.

But as the administration launched its new counter­offensive against Islamist militants in Iraq and Syria this week, the arm-and-train approach has emerged as one of the cornerstones of the president’s military plans for confronting the extremists groups in the region.

The sharp policy reversal is one measure of the brutal and rapid rise of the Islamic State and the limited options available to Obama in trying to confront the threat that the group has become.

The program to support the Free Syrian Army — which Saudi Arabia has now offered to host — is also one of the central tenets of the diplomatic outreach to Sunni Arab states, which will play a key role in checking the terrorist group’s progress on the ground.

The new approach is also one of the few administration proposals that enjoy bipartisan support on Capitol Hill. Lawmakers would be much less enthusiastic about any plan that called for U.S. combat troops on the ground in Syria and Iraq.

Here are key moments from the speaker of the House's news conference following President Obama's speech on America's efforts to combat Islamic State militants. (AP)

Jane Harman, president of the Woodrow Wilson Center for International Scholars, said the president and his advisers have concluded that ramping up support represents their best chance of fighting the terrorist group — also known by the acronyms ISIS and ISIL — in Syria while ensuring other extremist factions do not take their place.

“If ISIL is pulled out of the ungoverned part of Syria, somebody has to hold that ground,” said Harman, who had dinner with Obama and his national security team Monday night. Syrian President Bashar al-Assad “is not going to be able to do that, nor would they want him to do that. . . . Who can hold the territory? The least bad answer is not ISIL, and not some other extremist terror group.”

The administration formally asked Congress for the authority and funding to expand the training program in late June, as part of its overseas contingency operations request. Now the White House is asking lawmakers to provide what press secretary Josh Earnest described as “urgently needed authority” for the Pentagon to train and arm the rebels under a stop-gap spending bill scheduled for a House vote next week.

Senior administration officials — as well as several outside experts who have spoken to them in recent days — said a few factors have made arming the opposition more palatable than it was previously. The CIA has been supporting the Free Syrian Army in a limited capacity for more than a year, and that has given U.S. officials a chance to vet the rebels and their rivals more closely.

The fact that several regional Arab partners are willing to join in the effort, and that U.S. military airpower will help tip the scale on the battlefield, also made them more optimistic.

Part of the hope, according the individuals familiar with the administration’s thinking, is that if the Islamic State is sufficiently degraded, some of the Sunnis fighting with another extremist opposition group, Jabhat al-Nusra, will decide to join the Free Syrian Army’s ranks.

State Department spokeswoman Marie Harf acknowledged to reporters Thursday that additional support for the moderate rebels would not automatically ensure victory there. “To be clear, in Syria, it’s a very tough fight, though,” she said.

Vikram Singh, a former Obama administration official at the State and Defense departments, was among a small group of outside experts who were invited last week to meet with senior White House officials, including Chief of Staff Denis McDonough and national security adviser Antony Blinken, who briefed them on the administration’s plans.

“They were cautious [before] for very good reason. It’s complicated by the fact that one, it’s hard to get reliable information, and two, there is infighting among the groups and they turn on each other,” said Singh, who is vice president for national security and international policy at the Center for American Progress.“They’ve done a lot more and they understand it much better. They understand the dynamics more. This is still a pretty difficult proposition to go in and train these guys.”

Shawn Brimley, a former Pentagon official, was serving at the National Security Council in 2012 when the administration began examining options to deal with the Syrian civil war and Assad’s escalating brutality. “There was a philosophy of, ‘Oh, if we just do airstrikes and aggressive training of the moderate rebels,’ it would naturally lead to the best outcome,” he said. But in the debate “there was a division from every side” about the potential unintended consequences.

“They’ve made the calculation that the cost of not doing this is much higher than doing it,” Brimley said. “Their calculation all along was that it was a disaster in Syria, a festering wound, but American intervention would probably make matters worse.”

Some Democrats and several Republicans, including the Senate Foreign Relations Committee’s top Republican, Bob Corker (Tenn.), said the White House should have worked more closely with lawmakers to provide funding after the Foreign Relations Committee passed such a measure in May 2013.

The administration submitted its request to expand the program on June 26, six days after the House had passed its annual Pentagon spending bill. Rep. Rodney Frelinghuysen (R-N.J.), who chairs the House Appropriations subcommittee on defense, said Wednesday that the proposal was “air dropped” into the debate.

Corker said he considered the administration’s renewed push for aiding the rebels as political. “Since they don’t want to come up and provide a lot of information and since there has been bipartisan support for arming the moderate opposition, maybe it’s because they thought this is the one piece that they could get a lot of congressional buy-in on without doing a lot of selling,” he said in an interview.

Speaking at the White House daily briefing Thursday, Earnest said he knows Obama’s opponents “have urged him to take more decisive action to arm the Syrian opposition sooner. . . . The president drew a different conclusion.”

Intensifying support for the rebels now is also a way to bolster support for the counter­terrorism campaign among several Arab states. Close U.S. partner Saudi Arabia did not disguise displeasure last year when Obama backed off on planned airstrikes in Syria in response to Assad’s use of chemical weapons. Saudi officials said then that Obama was paying too little heed to the chaos in Syria as the civil war there raged and was too reluctant to commit U.S. military power.

Kenneth Pollack, a senior fellow at the Brookings Institution’s Center for Middle East Policy, said the fact that Saudi Arabia announced Wednesday that it would host the train-and-equip program was “huge.”

“The countries we most need on board are the Sunni Arab states,” he said.

In Jiddah, longtime Saudi Foreign Minister Prince Saud al-Faisal flashed a wry smile when asked Thursday whether Obama and the United States finally see the Syrian situation as a dire threat.

“I only see agreement. I don’t see disagreement,” he said to laughter. Even Secretary of State John F. Kerry, who was sitting next to him, cracked a smile. “I see the agreement that we have about the present situation,” Saud said

Still, some Republicans say the administration’s shift was not big enough. And some Democrats, including Rep. Adam B. Schiff (Calif.), a member of the House Intelligence Committee, also expressed skepticism.

“I think we need to be realistic about what this fighting force can achieve and what it will take,” Schiff said. “It’s a multi­year prospect and the numbers are going to be modest compared” with radical Islamist groups including Jabhat al-Nusra and the Islamic State. “It’s not a cure-all. It’s going to take years and even then its impact is going to be modest. This may be as much about securing the fulsome cooperation of our allies as anything else.”

Heading into a closed-door briefing from top national security officials, several House Republicans said they worried that by only asking for authority for the Pentagon to run the program, the president was unnecessarily limiting his ability to wage war.

“I think it needs to be broader,” Rep. Matt Salmon (Ariz.) said of the approach. “I think that what we need to do is to have a comprehensive plan. I think that we need to have a declaration of war and if we’re going to defeat this enemy, it needs to be all in.”

But Earnest, speaking at the White House briefing, said that was yet another reason why the Free Syrian Amy may be able to defy expectations.

“Based on the decision that the president announced last night, these Syrian opposition fighters will now be operating with the backing of the United States military,” he said. “That is to say, these opposition fighters will have American aircraft taking airstrikes in support of their ground operations. There is no doubt that will significantly enhance their capability on the battlefield.”

Gearan reported from Jiddah, Saudi Arabia. David Nakamura, Ed O’Keefe, Paul Kane and Greg Miller contributed to this report.