Trump administration officials, anticipating the defeat of the Islamic State in its de facto Syrian capital of Raqqa, are planning for what they see as the next stage of the war, a complex fight that will bring them into direct conflict with Syrian government and Iranian forces contesting control of a vast desert stretch in the eastern part of the country.

To some extent, that clash has already begun. Unprecedented recent U.S. strikes against regime and Iranian-backed militia forces have been intended as warnings to Syrian President Bashar al-Assad and Tehran that they will not be allowed to confront or impede the Americans and their local proxy forces.

As regime and militia forces have begun advancing eastward, senior White House officials have been pushing the Pentagon to establish outposts in the desert region. The goal would be to prevent a Syrian or Iranian military presence that would interfere with the U.S. military’s ability to break the Islamic State’s hold on the Euphrates River valley south of Raqqa and into Iraq — a sparsely populated area where the militants could regroup and continue to plan terrorist operations against the West.

Officials said Syrian government claims on the area would also undermine progress toward a political settlement in the long-separate rebel war against Assad, intended to stabilize the country by limiting his control and eventually driving him from power.

The wisdom and need for such a strategy — effectively inserting the United States in Syria’s civil war, after years of trying to stay out of it, and risking direct confrontation with Iran and Russia, Assad’s other main backer — has been a subject of intense debate between the White House and the Pentagon.

Some in the Pentagon have resisted the move, amid concern about distractions from the campaign against the Islamic State and whether U.S. troops put in isolated positions in Syria, or those in proximity to Iranian-backed militias in Iraq, could be protected. European allies in the anti-Islamic State coalition have also questioned whether U.S.-trained Syrians, now being recruited and trained to serve as a southern ground-force vanguard, are sufficient in number or capability to succeed.

One White House official, among several who spoke on the condition of anonymity to discuss Syria planning, dismissed such concerns, saying: “If you’re worried that any incident anywhere could cause Iran to take advantage of vulnerable U.S. forces . . . if you don’t think America has real interests that are worth fighting for, then fine.”

The official said the expanded U.S. role would not require more troops, comparing it to “The Rat Patrol,” the 1960s television series about small, allied desert forces deployed against the Germans in northern Africa during World War II.

“With our ability with air power . . . you’re not talking about a lot of requirements to do that,” the official said. “. . . You don’t need a lot of forces to go out and actually have a presence.”

This official and others played down reports of tensions over Syria strategy. “No one disagrees about the strategy or the objectives,” said a second White House official. “The question is how best to operationalize it.”

The Pentagon, not the White House, made the decision to shoot down Iranian drones and a Syrian fighter jet in response to their approaches to or attacks against U.S. forces and their Syrian allies, this official said. “They shot down an enemy aircraft for the first time in more than a decade. That’s accepting a high level of risk,” the official said. “. . . We’ve done quite a lot since April that the previous administration said was impossible without the conflict spiraling.”

Ilan Goldenberg, a former senior Pentagon official now in charge of the Center for a New American Security’s Middle East program, agreed that the Obama administration “over-agonized” about every decision in Syria.

But Goldenberg faulted the Trump administration with failing to articulate its strategy. “It has been the worst of all worlds,” he said. “A vagueness on strategy, but a willingness to deploy force. They are totally muddying the waters, and now you have significant risk of escalation.”

“I know the president is fond of secret plans,” Goldenberg said. “But this situation requires clarity about our objectives and what we will or won’t tolerate.”

Trump promised during his campaign to announce within his first month in office a new strategy for defeating the Islamic State. That strategy remains unrevealed, and for several months Trump appeared to be following President Barack Obama’s lead in avoiding Assad, Iran and Russia and continuing a punishing assault on Islamic State strongholds elsewhere in Syria, as well as in Iraq.

In April, Trump broke that mold with a cruise missile attack on regime forces after their use of chemical weapons against civilians. Assad and his allies protested but did little else.

More recently, however, there have been direct clashes between the United States and the regime. Trump’s campaign calls to join forces with Russia against the Islamic State have largely disappeared amid increased estrangement between Washington and Moscow and investigations of Trump associate’s contacts with Russian officials.

Despite U.S. warnings, regime and militia forces have moved toward the Syrian town of Tanf, near the Iraq border, where U.S. advisers are training Syrian proxies to head northeast toward Deir al-Zour, the region’s largest city, controlled by the regime and surrounded by the Islamic State. It is a prize that the regime also wants to claim.

At the end of May, Syrian and Iranian-backed forces pushed southward to the Iraq border, between Tanf and Bukamal, where the Euphrates crosses into Iraq. In Iraq, Iranian-backed militias have, in small but concerning numbers, left the anti-Islamic State fight and headed closer to the border, near where regime forces were approaching.

On at least three occasions in May and June, U.S. forces have bombed Iranian-supported militia forces approaching the Tanf garrison. Twice this month, they have shot down what they called “pro-regime” armed drones, including one on June 8 that fired on Syrian fighters and their American advisers.

On Sunday, two days before the most recent drone shoot-down near Tanf, a U.S. F/A-18 shot down a Syrian air force jet southwest of Raqqa.

In response, Russia said it would train its powerful antiaircraft defense system in western Syria on farther areas where U.S. aircraft are operating and shut down the communications line that the two militaries have used to avoid each other in the crowded Syrian airspace.

“The only actions we have taken against pro-regime forces in Syria . . . have been in self-defense,” Gen. Joseph F. Dunford Jr., chairman of the Joint Chiefs of Staff, said this week.

Dunford also made clear that victory against the Islamic State in Raqqa, and in Mosul, where the U.S.-led coalition and Iraqi forces are in the last stages of a months-long offensive, will not mark the end of the war.

“Raqqa is tactical. Mosul is tactical,” Dunford said. “We ought not to confuse success in Raqqa and Mosul as something that means it’s the end of the fight. I think we should all be braced for a long fight.”

In a report Wednesday, the Institute for the Study of War, referring to intelligence and expert sources, said that the Islamic State in Raqqa had already relocated “the majority of its leadership, media, chemical weapons, and external attack cells” south to the town of Mayadin in Deir al-Zour province.

Neither the U.S.-led coalition and its local allies nor what the institute called the “Russo-Iranian coalition” can “easily access this terrain — located deep along the Euphrates River Valley — with their current force posture,” it said.

At the White House, senior officials involved in Syria policy see what’s happening through a lens focused as much on Iran as on the Islamic State. The Iranian goal, said one, “seems to be focused on making that link-up with Iran-friendly forces on the other side of the border, to control lines of communication and try to block us from doing what our commanders and planners have judged all along is necessary to complete the ISIS campaign.” ISIS is another name for the Islamic State.

“If it impacts your political outcome, if it further enables Iran to solidify its position as the dominant force in Syria for the long haul,” the official said, “that threatens other things,” including “the defeat-ISIS strategy” and “the ability to get to political reconciliation efforts.”

“For us,” the official said, “that’s the biggest concern.”

Thomas Gibbons-Neff contributed to this report.

https://www.washingtonpost.com/world/national-security/us-on-collision-course-with-syria-and-iran-after-fall-of-de-facto-islamic-state-capital/2017/06/21/b03d9620-55cc-11e7-ba90-f5875b7d1876_story.html?utm_term=.14177a6dd4c2