Republican Sen. Lindsey Graham and retired US Army Gen. Jack Keane reportedly tried convincing President Donald Trump to walk back his decision to completely withdraw US forces in Syria.

The duo attempted to persuade him to keep a contingency force in the country to help defend oil fields from Iranian interests, NBC News reported.

Graham has been outspoken in keeping US troops in Syria, claiming the abrupt withdrawal would abandon Kurdish allies and lead to a resurgence of ISIS.

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Republican Sen. Lindsey Graham of South Carolina and retired US Army Gen. Jack Keane reportedly tried convincing President Donald Trump to walk back his decision to completely withdraw US forces in Syria, and instead, persuaded him to keep a contingency force in the country to help defend oil fields from Iranian interests.

Graham, an ardent Trump ally; and Keane, a Fox News contributor, visited the White House twice and deployed visual aids for their campaign, according to NBC News. The two have served in the US military and have written hawkish opinion columns defending the president in recent months.

Two days after Trump withdrew roughly two dozen US special operations troops from the immediate vicinity of Turkey's assault in northeastern Syria on October 6, Keane went to the White House and showed Trump a map of the oil fields located in northern Syria, people familiar with the matter said to NBC News.

Keane made another trip with Graham on October 14, where the duo listened to a phone call between Trump and Turkish President Recep Tayyip Erdogan, NBC News reported. Keane and Graham were also privy to a phone between Trump and Kurdish-led Syrian Democratic Forces commander Mazloum Kobani Abdi, who is in the middle of a tense truce with Turkish forces.

Keane and Graham reportedly warned Trump that that the roughly three quarters of the oil fields that were located in US and Kurdish-occupied territories could be compromised by the Iranians once US forces left the country. Trump appeared receptive to the idea, and on Monday announced that a small number of US troops will remain in the country "to secure the oil."

Keane, a retired four-star general, continues to have ties with the president. Shortly after the 2016 US presidential election, Keane claimed that he was once a top pick to be Trump's defense secretary. Keane said he declined the offer due to personal issues from his wife's recent death. According to Keane, Trump asked him for a recommendation for another defense secretary, to which Keane replied with recently-retired Marine Corps Gen. Jim Mattis and former CIA director David Petraeus.

Read more: 'It's utterly pathetic': Democratic lawmakers are flabbergasted by Trump's 'tough guy' letter to Turkey

Chairman of the Board of the Institute for the Study of War, retired US Army Gen. Jack Keane, testifies during a joint hearing before the Terrorism, Nonproliferation, and Trade Subcommittee and Middle East and North Africa Subcommittee of the House Foreign Affairs Committee, July 15, 2014 on Capitol Hill in Washington, DC. Alex Wong/Getty Images

Following Trump's decision to withdraw US troops from northern Syria, the president faced fierce criticism from both political parties and former US military officials. Graham has been outspoken in keeping US troops in Syria, claiming the abrupt withdrawal would abandon Kurdish allies and lead to a resurgence of ISIS.

"This impulsive decision by the president has undone all the gains we've made, thrown the region into further chaos, Iran is licking their chops, and if I'm an ISIS fighter, I've got a second lease on life," Sen. Lindsey Graham said during a Fox News interview on October 7.

Officials and Trump's allies have employed maps and other visual aids with "killer graphics" to inform the president, then-CIA director Mike Pompeo said in The Washington Post.

"That's our task, right? To deliver the material in a way that he can best understand the information we're trying to communicate," Pompeo told The Post in 2017.

The officials in Trump's orbit framed the Kurdish-Turkey conflict in economic terms, rather than a military strategy, and alerted him of potential boon for Iran, officials said to NBC News. Officials reportedly added that they believed Trump would be more receptive to an emphasis against Iran, rather than Russia, who is poised to benefit from the chaos in Syria.

Graham's role in the idea that Syrian oil fields will be compromised by malignant forces, including ISIS, was first reported by The Wall Street Journal on Sunday. Some US officials voiced their confusion on the talking point following Trump's announcement.

"I don't know where all this oil infrastructure stuff is coming from," a senior US official said to Al-Monitor. "Maybe playing to what [Trump] wants here. We have not seized the oil fields."

Many of the Syrian oil fields were captured by ISIS during the country's civil war. After US-backed Kurdish allies evicted ISIS from their strongholds, the northern oil fields were either controlled by the SDF or the US, experts said to The Post. The northeastern oil fields reportedly were once believed to produce roughly 60,000 barrels a day.