Washington(CNN) President Donald Trump declared Friday that the US is doing "very well" in Syria as the Pentagon began moving personnel and armored vehicles for eventual deployment into the eastern part of the country.

Multiple defense officials tell CNN the military is in the initial stages of moving the vehicles to defend oil fields the President is now prioritizing. Details of the movements are being closely held due to potential threats.

US troops in Syria have focused so far on fighting ISIS and advising local forces, missions that have not required heavily armored vehicles. And though US forces have been present in the oil fields region, the calculation to bring in reinforcements now centers on the possibility that they may need to deter the Syrian regime and possibly Russian forces as well, these officials say.

Almost two weeks after Trump was engulfed by a firestorm of criticism for his decision to pull troops out of northern Syria, the administration is bending to its critics, particularly Republicans, tweaking its rhetoric in Washington and calibrating its presence in Syria while the military quickly tries to adapt.

New plans ahead

An adjusted Syria plan is expected over the weekend, the President's allies have told CNN, but already changes are clear.

Two days after Trump's Wednesday pronouncement that US forces had "defeated 100% of the ISIS Caliphate" and that Turkey, Syria, and others should ensure the terror group does not regain territory, Defense Secretary Mark Esper said Friday the US will remain to fight ISIS and is now strengthening its position in eastern Syria.

"We are reinforcing that position, it will include some mechanized forces ... the mission in Syria remains what the mission in Syria began with, it's always been about defeating the ISIS coalition," Esper told reporters in Brussels. "That is the core mission."

Trump had originally said the US would leave Syria but stay "in the region to monitor the situation." Iraq's refusal to let US troops stay long-term meant that plan had to be reconsidered. Republican fury, particularly after Turkey responded to the American pullback by attacking the Kurds allied with the US, forced a reconsideration.

The shift underway now on Syria "is consistent with the way the President operates," said Nora Bensahel, a visiting professor of strategic studies at Johns Hopkins University. "He states one thing and if it doesn't go over particularly well, he will modify and adjust it and make it look like it was the plan all along. He encountered enormous pushback on what a total pullout would mean for the fight against Islamic State -- what you're seeing now is the response."

On Wednesday Trump insisted from the White House Diplomatic Reception Room that, "we're getting out ... Let someone else fight over this long-bloodstained sand." But his Republican critics, including Senate Majority Leader Mitch McConnell, had been working hard behind the scenes to change the White House approach.

A day later, on Thursday, South Carolina Sen. Lindsey Graham went to a meeting in the White House Situation Room with Trump, eight to ten other GOP senators, Gen. Mark Milley, the chairman of the Joint Chiefs, and others. Esper made an appearance via video from Brussels, where he has been attending a NATO meeting.

Afterward, Graham told reporters that "I think there is a plan coming together that I could support. We are not there yet, but I was very encouraged." The new Syria plan will be "presented and developed over the weekend," he added.

A senior administration official told CNN that Trump "President has made clear that the United States remains fully committed to the enduring defeat of ISIS, which is critical to our national security." As part of that mission, the US will deny ISIS access to Syrian oil fields, "critical resources and revenue that could allow it to regain strength" and will continue to assist Kurds to do so, the official said.

In Brussels, Esper said that the Pentagon "always intended, as the President directed, to maintain a presence at the At-Tanf garrison," which sits on the border with Jordan -- a request by Jordan and Israel. "We are also considering how we also might re-position forces in the area in order to make sure we secure the oil fields."

'Defeat ISIS'

Protecting the oil fields is all "nested underneath the defeat ISIS campaign," Esper said. "We want to make sure they do not have access to the resources that may allow them to strike within the region, to strike Europe, to strike the United States. Otherwise, all the other forces are intended to return home."

Defense officials note that while it's clear the President now wants to keep troops in Syria for at least some time, it's not clear how long. Though the strategy is being portrayed as a continued anti-ISIS mission, Amb. Jim Jeffrey, the US Envoy for Syria and the Global Coalition to Defeat ISIS, suggested damaging and long-lasting impact from the President's haphazard policy moves on Syria.

America's Kurdish allies, the Syrian Democratic Forces, have lost ground, suffered casualties, seen more than 170,000 people displaced and many say they've feel betrayed by the US.

Russia, Turkey, Iran and Syria have all gained an advantage with the US pullback. Hardened ISIS prisoners have escaped and the US is unable to track their whereabouts.

"The Turkish incursion into northeast Syria is a tragedy, it was long standing US government policy in two Administrations to keep that from happening and we were clearly not successful," Jeffrey told the House Foreign Affairs Committee Wednesday. "ISIS is pitching this as a victory for them," he said.

The Pentagon said in a statement that "the US is committed to reinforcing our position, in coordination with our SDF partners, in northeast Syria with additional military assets to prevent those oil fields from falling back to into the hands of ISIS or other destabilizing actors," a reference to Iran.

Privately, however, military officials say there is nothing in place to address the possibility that Syrian or Russian tanks or aircraft might approach the oil fields. The plan for now, officials say, is to declare the US presence and warn other players not to get close.

Officials said it's now expected that the "mechanized" reinforcements Esper described will mainly be armored vehicles, such as Bradley Fighting Vehicles or Paladin howitzers. The officials said there is an armored brigade in Kuwait that could be used to provide the equipment and troops needed to protect the oil fields.

On Thursday, Graham said approvingly the President has been increasingly intent on keeping oil -- potentially $45 million to $50 million a month, he estimated -- out of ISIS' hands.

'Let's keep talking'

"It's adding a new strategic objective that hasn't been there before, which is denying Syrian oil to the enemy," Graham explained. Asked if he and other Republicans were emphasizing the oil fields to get the President to line up with his Republican critics and maintain a US presence in Syria, Graham laid out how one military step might lead to another.

Trump understands that "the oil is a key asset," Graham said, "so I said OK, let's keep talking. If the money goes to the right people, the SDF, that's a good thing, it keeps the ISIS fight going. So Mr. President, the oil field won't guard itself. And once you're on the ground, you might as well be on the ground with the capability to continue the ISIS fight. So we may be getting there. The key to all of this is air power."

Securing the oil fields will mean having people on the ground, Graham said, adding that Milley was looking at how to accomplish that. "It's gonna take some troops on the ground. But the main component is air power. The bulk of the force will be SDF, but there will have to be some of us," he said.