Washington (CNN) Republican Sen. Lindsey Graham said that based on a conversation he had with Defense Secretary James Mattis on Wednesday, Mattis "firmly" believes "the job in Syria is not yet done" despite the fact that President Donald Trump ordered a withdrawal of US troops from the country.

Graham, who just returned from a trip to Afghanistan, told CNN's Kate Bolduan on "At This Hour" on Thursday that he and Mattis spoke after Trump announced the decision, which Graham has strongly rebuked and called on the President to reconsider.

"Secretary Mattis is firmly in the camp of the job in Syria is not yet done. That abandoning the Kurds now will hurt us down the road," Graham told Bolduan, adding, "That ISIS could and probably will come back. And I think that's the universal view of both [Secretary of State Mike] Pompeo and Mattis."

In recent days, Mattis, Pompeo and national security adviser John Bolton have cautioned against a rapid and immediate withdrawal from Syria, according to people familiar with the discussions.

Graham said that although Trump serves as commander in chief, he would be better served listening to the advice of people he can trust.

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