Republican Sens. John McCain and Lindsey Graham came out of their meeting with President Barack Obama more optimistic and supportive of a plan of military intervention in Syria. It potentially lines them up as key allies for Obama in Congressional passage of authorization of military force. Both warned, however, that passage has a "long way to go."

McCain told reporters after the meeting that a vote that prevents military action in Syria would be "catastrophic." He said that U.S. credibility would be "shredded," since Obama said on Saturday that he has decided military action is appropriate.

And both McCain and Graham both expressed confidence that Obama's plan of more limited intervention than they had hoped for would both weaken Syrian President Bashar al-Assad and strengthen rebel forces.

Graham, meanwhile, warned of the consequences a failed vote would have and the message it would send to Iran in their proliferation of nuclear weapons:

At the end of the day this is a Syrian fight, but the outcome does not limit itself to #Syria. — Lindsey Graham (@GrahamBlog) September 2, 2013

If we don't get Syria right, good luck in convincing the Iranians to change their behavior and their drive for nuclear weapons. — Lindsey Graham (@GrahamBlog) September 2, 2013

Syria is a cancer that is growing in the region. And over the past 2 years Pres. Obama has allowed the situation There to become a debacle. — Lindsey Graham (@GrahamBlog) September 2, 2013

The meeting with McCain and Graham was part of a broad push by the White House to win Congressional support for their military plan.

McCain and Graham are both important votes in the Senate, because they represent two of the Republican Party's fiercest foreign policy "hawks." They support action, but they don't think Obama's current plan of limited airstrikes is enough.

And they want a strategy that will eventually lead to the toppling of Assad — something the administration says is not the goal of the current plan, as it could lead to a longer-than-anticipated engagement in the country.