The violence in Yemen entered a new phase Thursday: A regional proxy war, with Saudi Arabia leading a coalition of 10 nations in air strikes against Houthi rebels, who are backed by Iran and have forced Yemen’s deposed, U.S-supported president to flee the country. While Yemen had been teetering on the verge of a civil war, foreign intervention, chiefly by Iran’s adversaries in the region, signaled the coming of a conventional military campaign that threatened to engulf the tumultuous region.

The path ahead for the United States, which for years has launched counterterrorism operations and drone strikes on Al Qaeda’s branch in Yemen, looked grim. The last U.S. forces in Yemen pulled out earlier this week, leaving the Obama administration with a dramatically diminished capability to combat al Qaeda and ISIS militants who have rooted themselves in the war-torn country and pose a threat to the West, experts and lawmakers said.

In an interview, Senator Richard Burr, the chairman of the Senate Intelligence Committee, told The Daily Beast that unfolding events in Yemen portended a dire future for U.S. policy across the region.

Photos: Rubble and Grief on the Ground in Yemen

“We’re totally out. Forward looking, this is what the region is going to look like if we don’t take care of al Qaeda, we don’t take care of ISIL, we don’t take care of Iran’s involvement with the Houthis,” Burr said, using the government’s preferred acronym for the so-called Islamic State. “Yemen is going to be, in the president’s own words, a ‘model,’ [but] not of success, [instead] of absolute failure of our foreign policy.”

Burr was referring to prior public assurances from President Obama that despite an escalating crisis in Yemen and waning U.S. influence there following the upheaval of the Arab Spring, counterterrorism operations were still a model of success and would inform future missions.

“It’s a big setback,” Bruce Riedel, a former CIA officer with extensive experience in the Middle East, said of the rapidly deteriorating security situation in Yemen, which now more than ever seems in the grips of an outright civil war. “Without both a U.S. presence on the ground or a reliable ally, it will be much more difficult to target al Qaeda in the Arabian Peninsula,” Riedel told The Daily Beast, referring to the terror group’s Yemeni branch—the one that U.S. intelligence officials say is most capable of attacking in Europe and the United States. “Much of eastern Yemen will be a chaotic no-man’s-land where al Qaeda can operate.”

The United States withdrew about 100 Special Operations forces from Yemen on Monday, in the face of escalating violence and the Houthi advance, which President Abd-Rabbu Mansour Hadi seemed incapable of repelling.

That effectively brought an end to U.S. counterterrorism operations, most notably drone strikes targeting members of al Qaeda in the Arabian Peninsula, or AQAP, and removed the most significant weapon the Americans had for fighting the terror group on its home turf.

But Democratic Representative Adam Schiff, a member of the intelligence “Gang of Eight” that is legally required to be briefed on classified matters by the Obama administration, emphasized that a counterterrorism program will continue even in the absence of a physical presence.

“We have a counterterrorism program in countries where we don’t have the physical presence that we’d like,” Schiff told The Daily Beast. “We’re more reliant on our overhead architecture…[and] the intelligence services of our regional partners, so it’s certainly not what we would like, but we have to make do with what we can.”

The potential collapse of Yemen comes as Islamic militants across the Middle East and North Africa are gaining momentum amid the chaos of collapsing governments and social unrest.

Libya, where the United States helped topple dictator Muammar Gaddafi in 2011, has emerged as a prime training ground for ISIS. Moroccan officials said this week they’d uncovered another ISIS recruitment cell in that country.

U.S. efforts to rout the militant group in Iraq are stalling, forcing the Americans to back Iran with airstrikes.

And with the deadly attacks on the Bardo museum in Tunisia last week, militants proved that even countries that saw the blooms of democracy in the wake of the Arab Spring are not beyond militants’ reach.

The long-term concern, according to intelligence lawmakers, is a resurgence of al Qaeda in the Arabian Peninsula, which has long held a stronghold in Yemen.

AQAP is responsible for numerous attempts to target the United States, including the underwear Christmas Day bomber incident, according to the National Counterterrorism Center.

“If put in a situation that degenerates to the point where Houthis attempt to govern the whole country and awaken strong antagonism from the Sunni tribes, there will be ample space for AQAP to have a resurgence. And that’s of grave concern to us,” Schiff said.

At the Pentagon, officials conceded that the decision to withdraw its remaining troops from Yemen had “degraded” their decade-long effort to combat AQAP, but they vowed the U.S. military will continue to “hunt and kill terrorists.” At a briefing with reporters, Army Colonel Steve Warren, a Pentagon spokesman, said airstrikes against suspected AQAP would continue, despite the loss of an ally on the ground.

“In terms of our counterterrorism efforts, to the degree that we are able to identify people who pose an imminent threat to our country, I think we will still need to take action to make sure that doesn’t happen,” said Schiff, the top Democrat on the House Intelligence Committee.

But there was skepticism over future strategy from Republicans on Capitol Hill.

“There isn’t [a counterterrorism strategy]. Our troops left. I think you saw that, right?” Sen. Bob Corker, the chairman of the Senate Foreign Relations Committee, told The Daily Beast. “The counterterrorism strategy we had is gone. We have not had any communications with the administration relative to how they plan to move ahead.”

He added, “You saw the Houthis are moving down towards Aden. The president is evacuating. We’ve left, the 100 folks that we had there are gone. We’ve had no word yet from the administration as to what their plans are for the future.”

The Pentagon spokesman said U.S. officials would not say whether Hadi had left Yemen. He had fled to the southern port city of Aden last month after the Houthis overran the capital city of Sana’a and effectively placed him under house arrest.

There were no immediate signs from Washington that military force would be brought to bear in the conflict. Burr, the Senate intelligence committee chairman, was dubious about the prospects of an intervention improving the situation. “Who do you attack?” he asked. “Do you attack the Houthis? Do you attack ISIL? Do you attack al Qaeda? The difficulty is that everyone in Yemen that’s in conflict is an enemy of ours.”

With Southern Yemen in chaos, eyes are also turning now to Yemen’s border with Saudi Arabia, where that country’s military forces have been amassing for a possible strike against the Houthis, Riyadh’s longtime foes. Saudi air forces in Wednesday night began bombing targets in Yemen.

That may be good news for Hadi, but could deal another blow to U.S. efforts to fight al Qaeda and ISIS, which has also made advances in Yemen.

“The Hadi government and the Houthis are opposed to ISIS and AQAP. If both collapse, then into the vacuum you may have more [militants] pour in,” Jon Alterman, a former senior State Department official who now directs the Middle East Program at the Center for Strategic and International Studies, told The Daily Beast.

But the pressure had been mounting on Saudi Arabia and other Persian Gulf nations to attack the Houthi forces, who they say are backed by Iran.

“There is a growing consensus that this is the finger of Iran and it needs to be put down decisively,” Alterman said.

In the past few days, Riedel said, the Saudi Defense Minister, Prince Mohammed bin Salman, visited the border region with Yemen and announced expansion of Saudi naval and military bases in the area. Salman is the son of the Saudi king and, at 34 years old, believed to be the youngest defense minister in the world. He’s seen as a rising star within the Saudi national security establishment.

“The Saudis can’t defeat the Houthis and take back Sana’a,” said Riedel, who’s now a senior fellow at the Brookings Institution’s Center for Middle East Policy. “The Saudi army would get bogged down in the mountains of northern Yemen. But their Air Force could target Houthi command centers and supply lines. The Houthis and Saudis fought several border skirmishes a decade ago, the Houthis always prevailed.”

“The only good news,” Riedel added, “is that the Houthis are violently opposed to al Qaeda and will fight them with determination.”

For now, at least, experts judged that the Saudi maneuvers were likely defensive. “My contacts stress the buildup is defensive, to discourage any cross-border Houthi action. It may also be an effort to divert Houthi troops away from the advance on Aden,” Riedel said.

With the Yemeni government possibly collapsed and the U.S. left with few good options for combating Islamist extremists there, questions are being raised about whether the Obama administration pursued too narrow a strategy in its fight against al Qaeda and could have done more to stabilize Yemen.

“It highlights the challenges when the bulk of our strategy towards a country is a counterterrorism strategy,” Alterman said, and one that particularly relies on drone strikes.

“People involved in Yemen policy complained that a huge part of our policy was all about targeting” with drone strikes, he added. “When such a large part of the counterterrorism strategy is carried out from the air, it’s hard to move around the country and identify the allies you need.”

— with additional reporting by Nancy Youssef