Washington (CNN) A widening Turkish military assault on northeastern Syria and rising casualties are sharpening the focus on the domestic political calculation President Donald Trump made in effectively abandoning America's Kurdish allies in the war against ISIS.

The move, which went against advice from his own diplomatic and military advisers and pleadings from Republican senators, is a classic exhibit from Trump's school of from-the-gut, "America First" foreign policy making. And he's trusting his instincts that for all the potential damage to the nation's reputation -- especially if there's a Kurdish bloodbath -- this could deliver a political dividend.

"You know, we're getting out of the endless wars. Have to do it. And eventually somebody was going to have to make the decision," Trump said Wednesday, revealing the basic political calculation behind his strategy.

This decision could rebound against Trump, if it opens a security vacuum that lets ISIS regroup and undermines his claim to have crushed the terror group . And it already leaves him looking callous. He explained Wednesday for instance that the Kurds were "fighting for their land" as if that made them less worthy of US protection.

"As somebody wrote in a very, very powerful article today, 'they didn't help us in the Second World War, they didn't help us with Normandy,' " the President said in an extraordinary comment at the White House.

Trump has stirred a political hornet's nest. Even normally supine Republican lawmakers are chastising him. Evangelical leaders who praised him as a divine gift for his Supreme Court picks are now offering prayers he changes course.

And a senior defense official told CNN Wednesday that Turkey's operation had already had a "detrimental effect" on American counter-ISIS operations, which have "effectively stopped."

There are also fears that thousands of ISIS fighters may escape from prisons in Syria as the Kurdish forces guarding them turn their attention to the barreling Turkish advance. Grisly footage of fleeing refugees, the possibility of civilian massacres, and a US withdrawal that hands new regional clout to Russia and Iran could come back to haunt Trump.

But he made a promise.

In nearly three years in office, Trump has shown an unusual persistence in honoring campaign trail vows. Whether it is pulling out of the Paris accord on climate change, the Iran nuclear deal or defying Congress to fund his border wall, he has often flouted official advice and alienated himself from much of the rest of the world. Trump knows his viability rests on his core group of grassroots supporters who he will never disappoint.

That's why he hinted Wednesday that the Kurds and Turks were just like a myriad of other Middle Eastern tribes that want America to fight their wars.

"They've been fighting again for many, many years. They're bitter enemies. Have been always, probably, possibly always will be," Trump said, even as critics warned he had blood on his hands for leaving America's Kurdish friends at Turkey's mercy.

In essence, the Syria gamble reconfirms a core principle of this presidency -- and has something in common with his dealings with Ukraine that could lead to his impeachment.

For Trump, foreign policy is not a matter of national interest or an extension of American exceptionalism. It's a tool for personal political advancement. No one can say that the President tries to hide it.

Classic Trumpian chaos

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In many ways, Trump's new Syria policy is typical of his national security decision making in that it unfolded in confusion, led him to apparently contradict his own statements then saw subordinates try to produce some after-the-fact coherence to the situation.

Also, not unusually, it emerged after a call with a foreign strongman -- the kind of leaders that have exploited Trump's hero worship -- in this case Turkish President Recip Tayyip Erdogan. And it flew in the face of advice from aides, political allies and America's friends.

On Sunday night in a stunning statement, Trump announced that the long awaited Turkish incursion into northeastern Syria would start and that US troops would leave the immediate area.

But by Monday, he was threatening to "obliterate" Turkey's economy if it did anything "off limits."

The next day he tweeted: "in no way have we Abandoned the Kurds, who are special people and wonderful fighters."

On Wednesday Trump insisted that Turkey's attack was a "bad idea." Secretary of State Mike Pompeo then weighed in insisted that Trump did not "green light" Turkey's operation.

But Turkey said Wednesday that Trump knew exactly what had been planned all along, implying he had endorsed it in his call with Erdogan.

"President Trump and President Erdogan have reached an understanding over precisely what this operation is," Gulnur Aybet, senior adviser to the Turkish President, told CNN's Christiane Amanpour

"He knows what the scope of the scope of this operation is."

So, the result is confusion and incoherence. The world's sole superpower has abandoned its historic role as guarantor of global stability and its own foreign policy values.

"This is just chaos. We don't do strategy, we shouldn't be doing foreign policy by tweet," retired General John Allen, a former presidential envoy for confronting ISIS told Amanpour.

Wide reverberations

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Trump's decision making on Syria this week has wide reaching implications.

It's not the first time America has deserted the Kurds, but Trump's attitude this week suggests there is no longer any moral underpinning to US foreign policy -- even if such a concept was always relative considering various historical blots.

The US move will be seen in the region as yet another loosening of American leverage. It will please Russia, which has enhanced its own power in the Middle East at the United States' expense over the Obama and Trump administrations. While the stated goal of US policy is to turn back Iran's regional influence, the creation of a vacuum in northeastern Syria will also play into Tehran's hands.

Politically, Trump has reopened the schism between his own "America First" isolationist school of foreign policy and the neoconservative hawkish worldview he rejects.

Even his closest friend in the Senate, South Carolina's Lindsey Graham, is outraged and inked an agreement with Democratic Sen. Chris Van Hollen of Maryland on severe sanctions against Turkey.

Reverend Franklin Graham, normally a staunch Trump supporter, issued a n extraordinary tweet about the Kurds

"The Kurds are the ones who have been leading the fight against ISIS in Syria. Also pray for the Christians who the Kurds have been protecting," Graham tweeted.

"They could be annihilated. Would you pray w/me that Pres. ⁦@realDonaldTrump⁩ will reconsider? Thousands of lives hang in the balance."

It's highly unusual for Trump to get such criticism. But his calculation will be that evangelical voters -- as they have through his parade of personal scandals and sometimes loutish behavior will stick with him. After all, there's no alternative and the bond that Trump made with social and Christian conservatives -- to stock the Supreme Court with like-minded justices -- has been kept. Just like his other promise to bring troops home. Whatever the cost.