Sen. John McCain suggested on Sunday that the U.S. deal with Russia to remove chemical weapons from Syria will be difficult to enforce without the threat of force.

"It's not a matter of trust," McCain said. "It's a matter of whether it will be enforced. [Russia foreign secretary Sergei Lavrov] said 'there is nothing in this agreement about the use of force,' i.e. they will not agree to the use of force no matter what [Syrian President] Bashar Assad does."

McCain also noted that Russia hasn't assigned blame for the Aug. 21 chemical weapons attack that killed more than 1,400, and that the nation has been helping to arm the Assad regime.

“There is not a seriousness on the part of the Russians. We’re going to see the Russians facilitating the departure of chemical weapons while plane load after plane load of Russian aircraft coming into Damascus full of weapons and devices to kill Syrians."

McCain also said he would have stepped up support for the Free Syrian Army and provided weapons for moderate rebel fighters if he were president.