Republican Sen. John McCain claims the embattled regime of Bashar al-Assad may have turned the tide in the bloody civil war which so far has claimed nearly 100,000 lives.

"Right now, Bashar al-Assad is winning," McCain said earlier this week.

The assessment is the latest to question whether the Obama administration has waited too long to play a meaningful role in ending the violence, as the bloody war drags on, and the U.S. continues to weigh whether to escalate its involvement beyond nonlethal aid and humanitarian assistance.

Such questions are being raised amid reports by rebel forces, bloggers and humanitarian observers that Assad forces in the past several days executed roughly 150 people during a roundup of civilians along Syria’s Mediterranean coast. It was the latest outburst of violence in a war marked by a succession of shocking mass killings.

The Obama administration is openly wary of getting too deeply involved, with officials arguing that a heavy footprint in Syria could do more harm than good for the opposition. President Obama has so far declined to act on reports that chemical weapons were used -- a factor he has called his "red line" -- invoking the flawed intelligence that helped precipitate the start of the Iraq war.

The U.S. instead is pursuing a peace conference next month, as well as additional U.N. resolutions. But every day brings more violence, and concern that the effort to consolidate international opposition to Assad is flagging.

Though time may be running out, British Prime Minister David Cameron asked Obama on Monday to help put more pressure on Assad to resign.

And Turkish Prime Minister Recep Tayyip Erdogan was expected to reinforce that message during his meeting with Obama on Thursday in Washington.

After the meeting, the two leaders presented a united front during a Rose Garden press conference.

"We're going to keep increasing the pressure on the Assad regime and working with the Syrian opposition," Obama said, adding they both agree "Assad needs to go."

Obama said there's no "magic formula," but said he has a "whole range of options" and voiced optimism about the peace conference.

Turkey, which borders Syria, has been among the biggest supporters of opposition forces and humanitarian efforts – allowing troops to assemble in the country and providing a safe haven for an estimated 400,000 Syrian refugees.

However, Turkish leaders appear increasingly frustrated that other NATO countries have not done more. Such frustrations nearly reached a tipping point Saturday when the Syrian violence spilled over into the border town of Reyhanli, with a car bomb killing 50 people.

"Of course Syria will be our main topic,” Erdogan told Reuters and other news agencies before leaving for Washington. “Turkey has been damaged more than any other country."

Meanwhile, Israel has already launched a missile attack on Syria to stop Assad from transferring weapons to Islamic militants and on Wednesday suggested the possibility of another attack.

James Carafano, a foreign policy expert at the conservative-leaning Heritage Foundation, said Wednesday that the United States and its allies missed their window of opportunity because they should have learned earlier in the conflict which opposition forces to back. Jihadists have over the years joined the fighting fray, making any effort to arm and coordinate with the mainstream opposition all the more challenging. Obama himself voiced concern in March that the country could become a haven for extremists.

“A little bit of focus and attention would have made a big difference,” Carafano said.

Carafano agreed that the U.S. should have been more supportive of Turkey and said that relationship combined with other factors has put the U.S. “in a position of playing catch up.”

Though he was skeptical of claims about Assad winning, he acknowledged that Russia supplying him with weapons helps stave off defeat and that “nobody thinks he’s on his last leg.”

McCain, who has been among the most critical on Capitol Hill about the administration’s handling of the crisis, said that Assad indeed having the upper hand would put a peace agreement further out of reach because such an accord will happen only if Russia thinks Assad is losing and cannot stay in power.

“That gives me great pessimism,” he said.

Obama said in August that Assad using chemical weapons would cross a “red line,” and has repeated that position in the face of reports that chemical weapons were likely used. Obama says he wants to know more about the circumstance of the deployment of those weapons.

Though the president has not signaled a willingness to send U.S. troops into the Middle Eastern country, the United States has joined other countries in providing Syria with millions of dollars worth of humanitarian aid and non-lethal military equipment.

Democrats and Republicans largely oppose on-the-ground military intervention but suggested in recent weeks that the U.S. arm pro-western rebel forces.

McCain, who has also suggested a no-fly zone, argues Obama miscalculated by declaring a red line because that has allowed Assad to do most everything short of using chemical weapons – including the use of SCUD missiles on civilians.

McCain and others also say a victory for Assad and his Iranian and Hezbollah supporters will create more instability in the region.

“Every day that goes by more jihadists flow into the region, more instability takes place in Lebanon and the other surrounding countries and Hezbollah becomes more and more active,” he said. “Every day that goes by, the aftermath is going to become more and more difficult."

He and Carafano also expressed little optimism about a peace conference in June among related nations that Secretary of State John Kerry is trying to broker and could include Russian leaders and Assad.

“Although I wish them well,” McCain said.

The Obama administration says its goal continues to be the ouster of the Assad regime. White House Press Secretary Jay Carney said Wednesday that Obama and his team "are constantly evaluating the options" for helping the Syrian people and opposition. He noted that the U.S. is "by far the largest donor" of humanitarian assistance.

State Department spokesman Patrick Ventrell said the U.S. continues to work "very closely with the opposition," including in efforts to set up the peace conference.

The U.S. on Wednesday joined a majority of United Nations member states in approving a non-binding General Assembly resolution that calls for a political transition in Syria and condemns the regime of Assad for atrocities. Russia, Iran, North Korea, Venezuela and other pro-Assad governments voted against the measure, calling it unbalanced and a setback for efforts to resolve the crisis in Syria.