AP
Sen. John McCain speaking to reporters in Washington.
Their argument focused on McCain's suggestion ISIS would not be as dangerous as it is today if Obama had left more of a "residual force" in Iraq after the end of combat operations there.
Speaking shortly after the president made a primetime address to the nation outlining his plan, McCain said Obama's speech was a "weak argument." He also claimed mistakes made by the Obama administration enabled ISIS to gain power. When Carney, who departed his position as Obama's top spokesman this summer, disputed some of McCain's comments, the senator became visibly agitated and said Carney was making statements that were "patently false."
"You don't have the facts Mr. Carney, that's the problem," McCain said.
The high volume battle between the two men, which CNN host Jake Tapper subsequently described as a "showdown," began with McCain taking issue with Carney's suggestion the Free Syrian Army is more battle ready than it has been in the past.
"I'm astounded that Mr. Carney should say that the Free Syrian Army is now stronger," said McCain.
The FSA is one of the more moderate opposition groups fighting both ISIS and the regime of Syrian President Bashar al-Assad. In his speech, Obama said "strengthening" moderate elements of the Syrian opposition would be part of his strategy to fight ISIS.
McCain argued that the Obama administration previously rejected recommendations to provide further support to the FSA.
"Your boss is the one that, when the entire national security team wanted to arm and train them … he turned them down," McCain said to Carney. "Facts are stubborn things ... he made the unilateral decision to turn them down."
McCain, who has been a staunch critic of the Obama administration's foreign policy, went on to attribute the rise of ISIS to the fact more troops were not left in Iraq after the end of U.S. combat operations there.
"The fact that he didn't leave a residual force in Iraq, overruling all his military advisors, is the reason were facing ISIS today," said McCain of Obama.
ISIS grew in Syria during the ongoing civil war there against the regime of President Bashar al-Assad that began in 2011. More recently, the group has made territorial gains in Iraq.
Carney, who was announced as a CNN contributor Wednesday, responded by saying McCain wanted to keep American troops in Iraq "in perpetuity." McCain said he simply wanted a sufficient military presence there to "keep the situation stable" and maintain progress made following the troop surge of 2007.
"We had it won thanks to the surge. It was won," McCain said. "The victory was there. All we needed was a force behind to provide support, not to engage in combat."
Both McCain and Carney raised their voices and repeatedly interrupted each other. At multiple points, McCain accused Carney of making "false" statements. Based on the American troop presence currently in Iraq, which the White House has described as an effort to support the army there, McCain also said the president was being misleading when he said the fight against ISIS would "not involve American combat troops fighting on foreign soil."
"This is another falsehood the president is purveying," said McCain. "We already have boots on the ground, over 1000."
McCain argued "we need more" troops on the ground in Iraq "to help the Iraqi army rebuild its capabilities."
Overall, McCain said he "would favor" most of the plans outlined by the president in his speech. However, he also argued it was incorrect for Obama to suggest his strategy to fight ISIS would be similar to military operations in Yemen and Somalia. McCain said ISIS is a far more dangerous opponent than the groups the U.S. has battled in those countries.
"The president doesn't really have a grasp for how serious the threat of ISIS is," McCain said.