Secretary of State John Kerry is engaging in a full-court press to sway Democratic allies to back a strike on Syria, amid growing concern that Congress will reject President Obama's call to authorize military action.

The effort comes amid signs that liberal lawmakers and libertarian Republicans could block efforts to use force to punish Syrian President Bashar Assad for using chemical weapons.

Kerry on Thursday night took his case for intervention in Syria to MSNBC’s Chris Hayes, who openly opposes any military strike, and also penned an op-ed for the Huffington Post on Friday.

U.N. Ambassador Samantha Power will also speak Friday at the Center for American Progress, in hopes of swaying liberal support.

Kerry, a former anti-Vietnam war hero who famously threw his military decorations and dog tags on the steps of the Capitol after returning from that conflict, passionately told Hayes Thursday that he would put his personal credibility on the line in favor of strikes against the Syrian government.

“I feel confident that what I am doing is informed by my own lessons of war and informed by my own opposition to war, but informed also by my years of supporting certain military actions when they're important to the security of our nation,” Kerry told Hayes.

Recalling the two years he spent trying to stop the war in Vietnam, the former chairman of the Senate Foreign Relations Committee, said he didn't come to the point of supporting military action in Syria lightly but came to it by “facts and reason.”

“I am informed by Vietnam, not imprisoned by it,” he wrote in his Huffington Post op-ed. “And I am informed by Iraq, not imprisoned by it, either.”

Critics of the president’s calls to strike Syria charge that a military response could drag the U.S. into a prolonged conflict.

Kerry told Hayes though that the president sought only a limited action and denied he would pull the U.S. into another “war.”

“I've thought a lot about this. I know the lessons of war. I don't believe this is taking America to war,” he said.

Kerry downplayed his own vote to authorize military action in Iraq in 2002, saying he was “opposed” to that war and had been persuaded by misleading evidence.

“When I was a senator [I] opposed the president's decision to go into Iraq,” he told Hayes. “But we know full well how that evidence was used to persuade all of us that authority ought to be given.”

Kerry also sought to address concerns that the Syrian opposition contained extremist groups.

Hayes pointed to a new video Images that have surfaced in recent days of rebel groups executing naked Syrian military soldiers.

Kerry though said the U.S. could separate out the “moderate opposition” from more extreme elements.

The secretary of State said the U.S. would only support pro-Western groups and that the opposition elements would be vetted by “our friends” – including Turkey, Jordan, Qatar, Saudi Arabia and the U.A.E. “A lot of people are involved in that process,” said Kerry.

Kerry’s effort to shore up Democratic support comes after several liberal groups earlier this week voiced strong opposition to any military intervention in Syria.

MoveOn surveyed its eight million members and found 73 percent wanted their member of Congress to oppose military action in Syria.

“We will mobilize to make sure our members' and allies' voices are heard in Washington and will work to prevent this nation from getting on the slippery slope to another ill-advised and unnecessary war,” Anna Galland, MoveOn's executive director, said Tuesday.

Congress and the nation, Galland said, should not be forced into a false choice over military action or doing nothing.

She said the U.S. should be leading the way in engaging the international community while exploring other avenues, including negotiations, economic sanctions, diplomacy and promotion of humanitarian aid.

President Obama, in Russia for the G-20 summit, has called lawmakers to rally support over Syria and will address the nation on Tuesday.