"You haven't gotten one in more than 10 years - more than 10 years".
Trump posed for photos, shook hands and signed autographs with airmen during a scene that resembled photo-op visits of former commanders-in-chief in years past.
Mattis was supposed to continue leading the Pentagon until late February but Trump moved up his exit and announced that Patrick Shanahan, deputy defense secretary, would take the job on January 1 and he was in "no rush" to nominate a new defense chief.
The Kata'ib Hezbollah group, another PMF faction, also threatened that the Shiite militias would force the American withdrawal if necessary, Press TV reveals.
"We have secured a record increase to our military budget, and we are purchasing all of this great equipment - $700 billion a year ago; $716 billion - with a "b", with a 'b, '" Trump said. "We could make it 3%, we could make it 2%, we could make it 4%,'" Trump told the troops about the latest pay raise.
Qais Khazali, the head of the Iran-backed Asaib Ahl al-Haq militia that fought key battles against IS in northern Iraq, promised on Twitter that Parliament would vote to expel US forces from Iraq, or the militias would force them out by "other means".
While in Iraq, Trump indicated he would not rush to nominate a new secretary to replace Mattis, the first defence chief in decades to resign over policy differences with the president.
It was set to Lee Greenwood's God Bless the United States of America, a song that the President frequently plays at his campaign rallies.
"We'll be watching ISIS very closely", said Trump, who was joined by first lady Melania Trump, but no members of his Cabinet or lawmakers. "Parliament must clearly and urgently express its view about the ongoing American violations of Iraqi sovereignty", Salam al-Shimiri, a lawmaker loyal to the populist cleric Moqtada al-Sadr, said.
Trump has come under withering criticism from fellow Republicans, Democrats and global allies over his decision to pull out of Syria because he believed Islamic State militants have been defeated.
"We've knocked them out", he said.
Special Operations Command (SOCOM) did not immediately respond to a request for comment.
Shortly after President Trump's announcement last Wednesday, U.S. officials had said it was likely that the 2,000 U.S. troops in Syria could all be pulled out in 30 days. "But I said, 'We have to take care of our military'". The president also suggested the country could be used to launch attacks on ISIS in Syria, warning American forces could attack the group "so fast and so hard" that they "won't know what the hell happened".
The U.S. has had a volatile relationship with Iraq over the years. "It's been more than 10 years", he continued.
During Trump's visit to the base, he paused to take a selfie with U.S. Navy Lieutenant Commander Kyu Lee.