U.S. Senator John McCain arrives on a visit at a migrant center near the village of Adasevci Thomson Reuters Sen. John McCain called on Wednesday for increased military action in Syria to stop authoritarian leader Bashar al-Assad, whose regime has massacred hundreds of thousands of civilians and caused a global refugee crisis.

In an editorial for The Wall Street Journal, McCain, who is chairman of the Senate Armed Services Committee, made the case for US intervention in Syria.

The Obama administration has been reluctant to get more involved, and over the past five years, the conflict has escalated. Russia is now involved, running airstrikes in support of Assad, and Iran is also bolstering the regime.

"As bad as this conflict is now, it can get much worse — and likely will," McCain wrote. "It will produce millions more refugees, undermining regional stability and straining the social fabric of Western nations. It will strengthen an anti-American alliance of Russia and Iran. US credibility with our closest security partners in the Middle East will further erode. And it will provide ISIS, or its successor groups, fertile ground to radicalize Muslims, recruit and inspire them to fight, and provide them with dangerous battlefield experience."

He continued: "This is where the conflict in Syria is headed, and the administration still has no strategy to do anything about it. Its diplomacy is toothless. And there appears to be no Plan B."

President Barack Obama has been often criticized for backing down on his "red line" in 2013 when he declined to strike Assad regime facilities after evidence emerged of regime forces using chemical weapons against civilians. Instead of a military strike, the Obama administration brokered a deal with the help of Russia that was supposed to see the removal of Assad's chemical weapons.

Obama points to this now as a success.

"It continues to puzzle me, the degree to which people seem to forget that we actually got the chemical weapons out of Syria," he told New York Magazine in an interview published this month. "The notion seems to be that, 'Well, you should have blown something up, even if that didn't mean that you got chemical weapons out.' There continues to be, I think, a lack of examination of the fact that my decision was not to let Assad do whatever he wanted."

The president continued: "My decision was to see if we could broker a deal without a strike to get those chemical weapons out, and to go to Congress to ask for authorization, because nowhere has Congress been more incoherent than when it comes to the powers I have."

A medic holds a dead child after airstrikes in the rebel held Karam Houmid neighborhood in Aleppo, Syria October 4, 2016. REUTERS/Abdalrhman Ismail

Obama sought approval from Congress for wider military action in Syria at the time, but support for the plan was low.

But McCain wrote that the idea that Congress wouldn't approve broader military action now is false.

"The administration likes to pretend that Congress is not prepared to support a more forceful approach because of its lack of support for military action to enforce President Obama's red line in 2013," McCain wrote. "This is a myth. What many in Congress opposed was granting a reluctant president authority to conduct what Secretary of State John Kerry promised would be 'unbelievably small' airstrikes in the absence of a broader strategy to achieve US national interests in Syria. The US needs that broader strategy now."

McCain outlined what that "broader strategy" would look like:

"Any alternative approach must begin with grounding Mr. Assad's air power. It is a strategic advantage that enables the Assad regime to perpetuate the conflict through the wanton slaughter of innocent Syrians. The US and its coalition partners must issue an ultimatum to Mr. Assad — stop flying or lose your aircraft — and be prepared to follow through. If Russia continues its indiscriminate bombing, we should make clear that we will take steps to hold its aircraft at greater risk. And we must create safe zones for Syrian civilians and do what is necessary to protect them against violations by Mr. Assad, Mr. Putin and extremist forces."

The Arizona senator also advocated for providing more assistance to moderate rebels fighting Assad in Syria, noting that it's the "only way to isolate and target extremists on the battlefield."

If left as it is now, the conflict in Syria will "continue to threaten the US and destabilize the world," McCain concluded.

The war in Syria has been raging on for more than five years. Rebels who oppose Assad's oppressive rule have been trying to force him from power, and extremist groups have sprung up to take advantage of the chaos.

Experts and former defense officials have argued that backing down on the red line hurt US credibility in Syria, making it more difficult to help solve the conflict now.