Few announcements from the Trump White House have engendered such bipartisan outrage as the news that Turkey was preparing to attack Kurdish forces in Syria — and the U.S. would be getting out of the way.Why it matters: Soner Cagaptay, an expert on U.S.-Turkey relations and author of the new book "Erdogan’s Empire," tells Axios the offensive that began Wednesday will further strain a longstanding alliance that looks increasingly likely to rupture.The big picture: The divide between the NATO allies, Cagaptay says, has grown across "16 years of war in 2 of Turkey’s neighbors — Iraq and Syria."The war in Iraq, he says, solidified the views of many in the U.S. that Turkey wasn’t “a reliable ally," and in Turkey that the U.S. was a "faraway power" that "creates chaos and civil war that Turkey then has to deal with."A decade later, Turkey "turned a blind eye to radicals crossing into Syria" in its push to oust Bashar al-Assad. "These radicals morphed into ISIS," Cagaptay says.The U.S. then allied itself with the YPG, the Kurdish militia at the heart of the U.S.-backed Syrian Democratic Forces, to take on ISIS.But the YPG takes orders from the PKK, which the U.S. considers a terror group and Turkey's Recep Tayyip Erdogan views as a "mortal enemy," Cagaptay says.“Turkey and the U.S. both picked as their proxy a sworn enemy of their ally.”CagaptayThe view from WashingtonTrump’s announcement on Sunday night "threw into the open the tensions over Turkey policy inside Washington,” Cagaptay says. “You saw the military pushing back, you saw the Hill pushing back."Nikki Haley, Trump’s former UN ambassador, tweeted on Monday: "#TurkeyIsNotOurFriend.” Sen. Lindsey Graham (R-S.C.) warned that Turkey’s offensive would permanently "destroy" the relationship.That anger reveals two things, Cagaptay says. First, the "temporary, transactional relationship" with Kurdish forces was increasingly viewed in Washington as "a permanent, strategic one."Second, "dislike of Erdogan is so strong in certain circles in Washington, including the Hill, that it distorts Turkey policy," Cagaptay says.The view from TurkeyWhile Turkey is polarized on most issues, Cagaptay says, nearly 90% of the country backs Erdogan's fight against the YPG."I think many policymakers and analysts have forgotten that the idea that the YPG is different from the PKK is basically a fig leaf that the U.S. invented so it would not be giving weapons to a terrorist group," he continues."If you think the YPG and PKK are different, what Turkey is doing becomes completely unacceptable," he says.But if you agree they're the same, he says, this is a U.S. ally attacking its "sworn enemy."Meanwhile, resentment over the 4 million Syria refugees Turkey has taken in has been intensified by an economic downturn.“It’s forcing Erdogan to make it look like he’s doing something to address the refugee problem. And that something will be to repatriate some refugees into Syria,” Cagaptay says.The Turkish offensiveCagaptay refers to Turkey's offensive as "a war that is not a war" because he's not expecting "massive fighting and massive bloodshed."The offensive is focused on an Arab-majority corridor where Turkish troops will, by and large, "be welcomed," Cagaptay says. He doesn’t expect the YPG to confront them head-on at the border."So Turkey will drive a wedge into the YPG’s territory and make that wedge solidly Arab," in part by repatriating refugees, Cagaptay says.But, but, but: "Although I don’t expect a war of epic proportions, things could always go wrong.""There is always the risk of civilian casualties and collateral damage," he says."And I think if Turkey goes maximalist and expands its reach into solidly Kurdish areas, then it will face an insurgency."What to watchErdogan expects little international pushback for his Syria offensive, Cagaptay says. And as anger grows in Washington, he continues to rely heavily on his personal relationship with Trump.“But a relationship that hinges on personalities, Erdogan and Trump, will face long-term risks,” Cagaptay says. “You need agencies to trust each other again. You need bureaucracies to have faith in each other. And faith between the militaries has already been undermined.”The bottom line: "On a day-to-day basis, I wonder if one of these crises that’s coming up will actually rupture the relationship."