Sen. Lindsey Graham, R-S.C., is an outspoken supporter of the Trump administration. But on Wednesday, he fired off a series of criticisms aimed at President Trump, in response to the commander-in-chief's previous statements about the senator's foreign policy.

His comments came after the president dismissed Graham's criticism at a press conference, saying that the South Carolina senator would want the U.S. to stay in the Middle East for a "thousand years." He also claimed that Graham's constituents wanted to bring U.S. troops home rather than leave them in Syria.

Graham, considered a foreign policy hawk, has been critical of Trump's decision to pull U.S. troops from Syria and claimed the president was responsible for Kurdish deaths after Turkey's incursion into the country. Kurds worked with U.S. forces in recent efforts to beat down the Islamic State terror group in the region.

ON SYRIA, TRUMP ACCUSES GRAHAM OF WANTING 'TO STAY IN THE MIDDLE EAST FOR THE NEXT THOUSAND YEARS'

According to CBN, Graham refused to back down on the issue and warned that conflict in Syria could be a "defining moment" for Trump.

"I am looking for President Trump to change this. I will do anything I can to help him, but I will also become President Trump's worst nightmare," he reportedly said.

"I will not sit along the sidelines and watch a good ally, the Kurds, be slaughtered by Turkey and watch Iran move into Syria and become another nightmare for Israel. This is a defining moment for President Trump. He needs to up his game."

The senator also tweeted several times on Wednesday, warning that Trump's diplomacy could make Syria like Iraq after former President Barack Obama decided to leave.

In an apparent message to Trump, Graham said he would never be quiet on issues related to national security. He tweeted his fear that the Syria conflict could become a "complete and utter national security disaster."

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Graham added that Trump was in conflict not only with him, but also with his own advisers. "Mr. President, forget about what I’m saying about Syria," he tweeted. "Listen to your own national security team who are telling you the consequences of your decision and the impact it will have on our nation."