Syrian President Bashar Assad's government is angry Washington has not taken it on as a partner in the international campaign to hit the Islamic State group, likely for a very significant reason: It is worried that once the United States has crossed the Rubicon of airstrikes in Syria, it could next turn its sights on Assad himself, aiming for his eventual downfall.

Such a scenario may not be an imminent one, but it is bound to be rattling Damascus. Already, the American plan includes beefing up rebel factions to the biggest extent yet in the 3 ½-year war.

For now, analysts say Washington's aim beyond destroying the Islamic State group, which is also known by the acronyms ISIS or ISIL, will be to create a new dynamic on the ground that would put enough pressure on Assad to go back to the negotiating table.

"The campaign against ISIS is going to put a lot of pressure on the Assad regime and in the end, it's not going to just degrade ISIS, it's also going to degrade the regime's ability to resist a settlement that includes the departure of Assad himself," said Amr al-Azm, a professor at Shawnee State University in Ohio.

"It's going to further weaken the ability of Assad to survive. There's no way he's not going to get drawn into that," he said.

President Barack Obama said Wednesday his current strategy of striking in Iraq and Syria is focused on the threat posed by the Islamic State group. But he also hinted at something beyond when he said "the Assad regime will never regain the legitimacy it has lost."

"We must strengthen the opposition as the best counterweight to extremists like ISIL, while pursuing the political solution necessary to solve Syria's crisis once and for all," Obama said Wednesday.

The Syrian government has said it welcomes U.S. airstrikes against the Islamic State group in Syria. But it had been gambling that Washington would partner with it against the extremists, hoping for a dramatic reversal in the U.S. policy calling for Assad's removal.

After Obama's comments Wednesday made clear the U.S. is sticking with the rebels, Syrian Foreign Minister Walid al-Moallem said any U.S. military operations in Syria would be considered an aggression unless coordinated with the government in Damascus.

Assad has not directly commented on Obama's speech, telling the new U.N. envoy to Syria on Thursday that the top priority now was fighting terrorism. But his political adviser, Bouthaina Shaaban, made a series of media appearances Thursday night, saying Obama was making a big mistake by excluding the Syrian government.

She said the Syrian government was "very serious" in pursuing a political settlement for the Syria crisis.

Assad's government in key ways benefited from the Islamic State group's rise in Syria. Its brutality reinforced Assad's narrative that he is up against terrorists, not democracy-seeking Syrians. Over the past year, government forces were able to seize momentum in the civil war, recapturing territory, in part because of the infighting between the Islamic State group and other rebels. Assad's forces largely avoided hitting its fighters.

But more recently Assad has started to feel the heat from the Islamic State group. After initially focusing on defeating rival rebels in northern Syria, the group turned its attention to government troops, killing hundreds of soldiers and allied militiamen in the past two months after capturing army bases in the country's east.

The militants made a big display of humiliating and slaughtering the troops, posting online footage of soldiers stripped down to their underwear before they were shot dead, while beheading others and placing their heads on poles.

Posters of martyred soldiers line the streets of government strongholds such as Lattakia and Tartous, centers for the minority Alawite community to which Assad belongs. Many soldiers are still missing. The soaring death toll has led to renewed soul searching and immense pressure on Assad among Alawites, for whom the losses constituted a severe psychological and moral blow. There have been several incidents of Assad loyalists protesting against the government recently.

Mudar Khadur, an Alawite government supporter and lawyer from Tartous, was arrested earlier this month after launching a social media campaign entitled "Waynon?" — Arabic for "Where Are They?" urging the government to come forth with information on the fate of missing soldiers.

"The Syrian regime has realized too late that it has made itself exposed and vulnerable to ISIS by allowing it to operate relatively freely," said Lina Khatib, director of the Carnegie Middle East Center in Beirut. She said that popular anger, however, is still not significant enough to form a real threat to Assad simply because of lack of alternative.

Assad also faces a manpower crisis because many of the Shiite Iraqis he was relying on as fighters on front lines around Damascus have returned to Iraq to fight there. Hezbollah, whose fighters have helped Assad's forces regain ground from rebels, has been sucked into ongoing battles with Sunni extremists near the border with Lebanon.

Assad may also feel the heat from regional realignments brought about by the Islamic State threat. The Iraqi model, whereby a Shiite prime minister backed by Iran and Syria was recently forced to step down peacefully, is a formula the West may eventually want to repeat in Syria to allow a transitional government.

"These changes in reality on the ground are now making Assad really feel the pinch in a way that he hasn't felt before," said al-Azm.

Analysts say that while the U.S. may view its current engagement as one focused solely on the Islamic State group, regional allies including Saudi Arabia — which has agreed to open its bases for the training of moderate Syrian rebel forces — view it as a tool to eventually oust the Assad regime.

Much of their future cooperation with the U.S. will hinge on whether they see Washington getting serious about supporting the opposition.

"There are serious problems here for the regime and I think that the Americans this time are going to keep the heat up to drag Assad to the table," said al-Azm.

"This is where the danger is for Assad."

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EDITOR'S NOTE — Zeina Karam is the AP's bureau chief in Beirut and has covered Syria since 1996.