The effectiveness of the US-led coalition effort in Syria is under scrutiny as Islamic State fighters try to overrun a strategic Syrian town on Turkey's border.

The United States and its allies, including Gulf states, have conducted more than 130 airstrikes in Syria against Islamic state militants since September 22, in the biggest show of Arab support for US-led military action in the Middle East since the 1991 Gulf War.

Reuters interviews with current and former administration officials show that the coalition was still taking shape even as President Barack Obama approved the US military's plan on Thursday, September 18.

"It wasn't clear Thursday morning that you would have five countries flying with us," a senior Obama administration official told Reuters. "(Obama) explicitly wanted to have the biggest coalition possible. And that was part of the reason why it took several days to initiate strikes."

The result -- the United Arab Emirates, Saudi Arabia, Jordan and Bahrain carried out air strikes alongside the United States, while Qatar flew a defensive mission -- allowed Obama to declare the morning after the strikes that "this is not America's fight alone."

The support of his fledgling coalition and backing of Congress forged during those days will be tested during a long-term effort in Syria that may outlast Obama's presidency.

'YOU'RE GOING TO DESTROY THE ADMINISTRATION'

When Obama declared on the night of September 10, in a televised address, that he would not allow the Islamic State a "safe haven" in Syria, he was explaining to Americans a policy shift he and his advisors had already been quietly detailing for days to members on Congress and their staff.

Their lobbying focused on US military plans to train and equip moderate Syrian rebels, who Obama hoped, in time, would be able to take territory back from the Islamic State. He needed Congress to authorize the training before it went into recess on September 19.

"We want to move fast and we're sending the language over," Lisa Monaco, Obama's counter-terrorism adviser, told Republican Representative Buck McKeon, the chairman of the House Armed Services Committee, a person familiar with the exchange said.

The urgency was a turnabout for the Obama White House. Long wary of the Syrian rebels, Obama and his aides had sent a proposal for training the rebels to Capitol Hill months before but did not lobby for it aggressively at the time, congressional aides and former U.S. officials said.

Obama personally met congressional leaders the day before his speech, assuring them that he would not deploy American ground troops. The top Republican in Congress, Speaker of the House of Representatives John Boehner, went along with the plan, which was key to winning enough support from his party to pass the measure.

Representative Adam Smith, the top Democrat on the House Armed Services Committee, described the administration's outreach as "very aggressive" and couched in reassurances that Gulf allies would be there.

"So it would not be just us sticking our neck out. It (the anti-IS push) would be in coordination with our local partners," Smith said.

Smith said he had several calls from Susan Rice, White House National Security Advisor, and even one call from Obama. All had the same message: "Please pass this."

The political stakes for Obama were hard to understate -- particularly after Congress balked last year when he presented plans for airstrikes to punish Syrian President Bashar Al-Assad for using chemical weapons against his own people.

As the House debated the amendment to allow for the training, a member of the Democratic leadership admonished one member who said he would vote his conscience.

"You're going to destroy the administration," the lawmaker said, punctuating his remarks with a curse, according to an aide who was told about the exchange.

The measure passed the House of Representatives on September 17 and the Senate on September 18.

FOLLOW THROUGH

One of the challenges for Obama going into the battle against Islamic State was to convince allies in the region that the United States would actually follow through with threats of military action.

Only a year earlier Obama had shied away from airstrikes in Syria over Assad's use of chemical weapons, and his Sept. 10 speech was not followed by any immediate action in Syria. At one point, aides used phrases such as "if the president" chooses to act.

Secretary of State John Kerry was tasked with repairing damage to U.S.-Saudi ties, which had been strained by Obama's long reluctance to get militarily involved inSyria. Kerry had been laying the groundwork for this with Saudi officials from King Abdullah on down during a series of trips to the region.

Initially, the Saudis made no effort to hide their suspicion that in the end, Washingtonwould do nothing, U.S. officials said.

But over time, minds began to change. A critical moment came shortly after Obama's Sept. 10 speech in which he said for the first time he was prepared to take action inSyria.

Kerry was in Jeddah, Saudi Arabia, meeting with Arab officials. Behind closed doors at Jeddah's Royal Terminal, he huddled with foreign ministers from Saudi Arabia,Qatar, Bahrain, Oman, Kuwait, Egypt, Iraq, Jordan, Lebanon and Turkey, along with a senior official from the United Arab Emirates. The meeting was scheduled to last two hours. It went on for more than five.

Lebanese Foreign Minister Gebran Bassil told Reuters there was extensive discussion about whether the campaign should be broadened to include jihadist groups beyond Islamic State. That was something that strongly anti-Islamist Gulf Arab states such as the United Arab Emirates had sought, but Turkey - an ally ofEgypt's outlawed Muslim Brotherhood - opposed.

"Everybody has their worries and are asking to the extent which we should go, not only to include Islamic State in Syria and Iraq but also sister companies of Islamic State, everywhere," Bassil said.

In a hint of the friction that would later define Washington's cooperation with Ankara,Turkey's foreign minister did not sign the Jeddah communique.

At the time, US officials explained Turkey's reluctance by noting its unique "sensitivities," including 46 Turkish diplomats and their family held hostage by Islamic State. Their release on September 20, however, has done little to sway Ankara into bolder action.

After Kerry's lengthy discussions with Gulf Arab officials, he held a crucial meeting atJeddah's Royal Palace, where King Abdullah typically spends the summer months. It was late, just after 9 pm, when he arrived.

He was joined by State Department deputy chief of staff Jon Finer, Assistant Secretary Anne Patterson and Robert Malley, a senior director at the National Security Council.

During this session, which stretched into the night, Abdullah said he was "willing to do whatever was necessary to help with the coalition, including air strikes," according to a senior State Department official.

A Western diplomat said that by the time the Jeddah meeting took place, the UAEwas giving the strong impression that it would be prepared to "open everything" in terms of its military facilities to support a campaign against Islamic State, in the event that such a broad coalition was finally agreed.

Still, the level of participation in strikes by each Gulf partner would take time to hammer out.

GEARS IN MOTION

Part of that responsibility fell to General Lloyd Austin, head of US Central Command, who conducted his own campaign to build support for Arab strikes, visiting Saudi Arabia, Qatar, the UAE and Jordan in the days before he presented Obama military options.

In addition to courting Arab nations' general support, "he also encouraged their active involvement in the conduct of the strikes," a defense official said.

The gears on military commitments began to turn more quickly after Austin briefed Obama at CENTCOM headquarters in Tampa, Florida, on Wednesday, September 17.

According to one official, who spoke on condition of anonymity, Austin explained at that meeting how strikes in Syria would ultimately help degrade the Islamic State's capabilities to act in Iraq.

At the Oval Office the next day, Obama approved the plan. "But his instruction was to aim for the broadest possible Arab backing and the initiation of strikes," the first senior administration official said.

In giving the green light, Obama had to overcome his hesitation to getting entangled in Syria's civil war, but aides said he recognized it was not a question of whether to conduct operations in Syria but how to do it as a way to deny a safe haven to Islamic State in Syria.

The president and his team had begun to look at the possibility of airstrikes after the militant group beheaded two American captives, macabre episodes that led American public opinion to abruptly shift in favor of action.

The United States moved ahead, incorporating the UAE in the air strikes and, as those plans progressed, other partners into the battle plan, officials said. Qatar was the last to sign up but said it would not fire weapons.

The United States informed Iran of its intention to strike Islamic State militants inSyria but not the forces of Syrian President Bashar al-Assad, a senior Iranian official said. The United States denied disclosing timing or targets.

Syria's UN Ambassador, Bashar Ja'afari, told Reuters he was personally informed by US Ambassador Samantha Power in advance of US and Arab airstrikes against Islamic State targets. Washington has denied any military coordination with Syria.

When the coalition jets took to the air, Syria did not employ its air defenses to target them. A top Pentagon official described Syria's radar acquisition as "passive."

The first wave of strikes began at about 8:30 pm Washington time. The USS Arleigh Burke guided missile destroyer in the Red Sea and the USS Philippine Sea guided missile cruiser in the Gulf fired more than 40 Tomahawk cruise missiles into eastern and northern Syria.

The second wave of strikes began 30 minutes later and included the US F-22 Raptor stealth jet in its first combat role, along with bombers, drones and other fighter jets that hit Islamic State headquarters, training camps barracks and combat vehicles in northern Syria.

Although the second wave included some coalition support, the third and final wave of strikes had the largest number of coalition aircraft in the air, about half of the total, the Pentagon said.

Although most of the firepower came from U.S. ships and aircraft, the participation of Arab partners "gave us more flexibility in targeting," one official said.

Another official said existing targets inside Syria were matched up to partner capabilities.

Austin, in comments sent to Reuters, called the operation "historic." But he also cautioned about the long road ahead.

"We're not spiking the football," he said, referring to how American football players celebrate when they score a touchdown.

"There's a lot of work still to be done and we need to keep the coalition together and stay focused on the objective." - Reuters