Sen. John McCain (R-Ariz.) said Sunday that President Obama's "red line" on Syria was written in "disappearing ink."

"Unfortunately, the red line that the president of the United States [has] was apparently written in disappearing ink," McCain said on "Fox News Sunday."

The Obama administration recently told Congress there is evidence that chemical weapons have been used in Syria, something that Obama has referred to as a “red line.” Last week, Defense Secretary Chuck Hagel said the Obama administration is rethinking its opposition to arming rebel forces in Syria who are opposing the government there.