Turkey has proceeded with its acquisition of Russian S-400 missiles, despite protests from the United States. Ankara’s decision to source anti-air missiles from Russia raised eyebrows in Washington when the deal was initially announced. Now that deliveries of the $2.5 billion weapons-package have begun, there is a lingering question of how to respond to the perceived slight. Some members of the US Congress are pushing for sanctions, which both the US Department of State and the Pentagon have officially said will be forthcoming. However, US President Donald Trump has wavered on whether he would punish Turkey or not and, considering his friendship with Turkish President Recep Tayyip Erdogan, it’s not inconceivable that he lets it slide.

Originally, Turkey had spent the latter years of Obama’s final term negotiating a contract for the American-made Patriot missile system, but a pact failed to materialize. To further complicate matters, an unsuccessful coup was not met with an international response that Erdogan felt was appropriate. Shortly before the failed ouster took place, both Germany and the US removed their Patriot systems from the nation. When the day finally came, jets were ordered from the Turkish Murted air base to strike government targets. The symmetry of both of these events appears to have left an impact on Erdogan; the first deployment of S-400 missiles are allocated for Murted air base.

Ever the businessman, Trump did his best to sway Erdogan towards purchasing US missiles, even offering a discounted rate, yet nothing seemed to lure Ankara. Its purchase of Russian weapons has not only angered US officials, but also other NATO members. There is a legitimate security concern with Turkey using the Russian missile system, as they would need to be programmed with the identification codes for NATO military aircraft. It is not much of a stretch to imagine that this data could leak back to Moscow, imperiling NATO jets.

While Trump filled Twitter with threats of punishment against Ankara should it continue with the Russian deal, he spoke softer when he met Erdogan at the G-20 Summit in June. There, he shifted the blame to former US President Barack Obama, as he explained that his predecessor refused to even consider making a deal until Turkey had already been courted by Russia.

“You can’t do business that way. It’s not good. He is a NATO member, he’s somebody that I have become friendly with. I don’t think he was treated fairly,” Trump said following the G-20 meeting. “We’re looking at different solutions.”

His revisionist history lesson aside, neither Trump nor his administration have publicly discussed the “different solutions.” Under the Countering America’s Adversaries Through Sanctions Act, Trump is required to choose a minimum of five secondary sanctions from a list of 12 on Russian businesses. One such entity included in the law is the producer of the S-400, Rosoboronexport. The CAATSA was signed into law by Trump in 2017 with a primary focus on providing the means to punish North Korea, Iran, or Russia through economic means. The president can, however, activate a provision of the law that allows for avoiding sanctions by citing security interests, which could be a valid point in Turkey’s case, as the US has a highly-strategic military base in the city of Adana, which maintains part of NATO’s nuclear arsenal, some of the only weapons of their kind in the region.

Imposing sanctions on Turkey also is within Trump’s power, although they could have the opposite effect than what is intended. At the heart of the issue is Turkey cozying up to Russia instead of its NATO allies. Sanctioning Turkey would only create more discontent and provide another reason to choose Russia as a supplier for future deals, effectively increasing Russia’s sphere of influence in the region. Trump has already flexed CAATSA once before on China’s Equipment Development Department. Like Turkey, Beijing had ordered S-400 equipment and Russian Su-35 jets.

Already, the US Congress and Department of Defense have made it overwhelmingly clear that Turkey’s purchase of Russian defense equipment disqualifies it from acquiring the NATO-developed F-35 stealth fighter. The US has suspended the training of Turkish pilots, threatening to remove them from the country by the end of July, and held its first F-35 CEO roundtable without Ankara’s participation. It’s very safe to say that deliveries of the aircraft are halted indefinitely.

“It’s impossible under our law… we also, a couple of days ago, passed legislation banning the sale of the F-35 to Turkey if they activate the Russian S-400 missile battery,” said Senator Lindsey Graham, a longtime Trump ally. “There’s no way we’re going to transfer to Turkey the F-35 technology and let them buy a Russian missile battery at the same time…under our law, there is no discretion.”

The Trump administration now must decide how it can appropriately punish Turkey. NATO allies and other Middle Eastern states will base their future actions on the US response. If it hits back too hard, it might push Turkey and other nations to deal more with Russia. If Trump’s retaliation is too soft, the US will look weak. There is also Iran to consider: if Washington is so eager and forceful against Tehran based on its security threat, how can it also go weak on Ankara over a similar issue?