Trump's homeland security advisor Tom Bossert said the U.S. would prefer Turkey exit from Afrin, Syria, where it's been launching an assault on U.S.-backed Kurdish forces. That's a shift from just earlier this week when U.S. Secretary of State Rex Tillerson said he hoped Turkey would exercise "restraint" in the offensive.

What's happening: Turkey's entrance for the first time as an overt combatant in the war is dramatically shifting the political calculus of the war, and exposing a new challenge for the Trump administration: delineating the boundaries, physical and otherwise, of U.S. involvement in Syria post-ISIS.

The big picture is this reveals how little influence in the region the U.S. now holds, former Senior Adviser to the Bureau of European and Eurasian Affairs at the U.S. State Department, David Phillips, tells Axios.

is this reveals how little influence in the region the U.S. now holds, former Senior Adviser to the Bureau of European and Eurasian Affairs at the U.S. State Department, David Phillips, tells Axios. This cements , “at least in near term, that Turkey and Russia will work against the U.S. in the region for an outcome that is damaging for U.S. national security,” Jenny Cafarella, the Senior Intelligence Planner at the Institute for the Study of War, tells Axios.

, “at least in near term, that Turkey and Russia will work against the U.S. in the region for an outcome that is damaging for U.S. national security,” Jenny Cafarella, the Senior Intelligence Planner at the Institute for the Study of War, tells Axios. Turkey coordinated with Russia to de-conflict the area so that Turkey could launch the assault in the first place, even though Russia and Turkey hold different beliefs about what Syria's future should hold.

to de-conflict the area so that Turkey could launch the assault in the first place, even though Russia and Turkey hold different beliefs about what Syria's future should hold. The bottom line, per Cafarella: “If the U.S. is indirectly at war with Turkey the U.S. will have a hard time” pivoting to broad goals, such as getting Assad booted from power.

State of the conflict in Afrin

"The Turkish army is besieging Afrin from three sides," Rezan Hiddo, a Kurdish official in Afrin told the AP.

The chief of the U.S. Central Command Gen. Joseph Votel and the White House envoy for the war against ISIS Brett McGurk are in Syria this week talking with Kurdish officials, per the AP.

Gen. Joseph Votel and the White House envoy for the war against ISIS Brett McGurk are in Syria this week talking with Kurdish officials, per the AP. Turkey’s stated objectives are to seize Afrin and then move the offensive towards Manbij. If that happens, it raises the prospect of direct clashes with U.S. forces.

The U.S. shifts

U.S. Secretary of State Rex Tillerson announced last week the U.S. would be bolstering a border force, which alarmed Turkey and provided some rationale for the assault.

announced last week the U.S. would be bolstering a border force, which alarmed Turkey and provided some rationale for the assault. A State Department official then walked Tillerson’s comments back and pointed out that the operation in Syria remains one of support and stability.

then walked Tillerson’s comments back and pointed out that the operation in Syria remains one of support and stability. Yes, but: A stabler YPG force is exactly the opposite of what Turkey wants. This pits the U.S. against Turkey so long as the U.S. backs the YPG.

A stabler YPG force is exactly the opposite of what Turkey wants. This pits the U.S. against Turkey so long as the U.S. backs the YPG. It was a question of when this would happen, not if. Turkey has been posturing to counter the YPG for some time now, and the U.S. has long-known Turkey views the YPG as a terrorist organization.

Turkey has been posturing to counter the YPG for some time now, and the U.S. has long-known Turkey views the YPG as a terrorist organization. The White House said Trump discussed concerns with Erdogan that the assault erodes U.S. and Turkish goals in Syria. Turkish officials told the AP Trump did not express concerns over escalating violence.

What now

Phillips predicts a more hands off approach from the U.S. moving forward: “I’m just waiting for the next foot to fall,” Phillips said. He says he thinks the U.S. will “do the same” thing that it did to the Iraqi Kurds in Kirkuk (allowing rivals in, such as the IRGC in that case, in to reduce the Kurds' gains). He expects it will happen “to the Syrian Kurds as soon as its expedient" for the U.S.

moving forward: “I’m just waiting for the next foot to fall,” Phillips said. He says he thinks the U.S. will “do the same” thing that it did to the Iraqi Kurds in Kirkuk (allowing rivals in, such as the IRGC in that case, in to reduce the Kurds' gains). He expects it will happen “to the Syrian Kurds as soon as its expedient" for the U.S. On whether a political solution is possible now: Right now, not really, per Phillips. It’s “hard to get to that point when there’s active hostility going on. That’s why Turkey’s entry into Syria as an overt combatant is such a problem" for the U.S.

Scheduled diplomatic talks lie ahead, which Cafarella says could help the U.S. “preserve gains that we’ve built and realign with Turkey.”