Relations between the U.S. Turkey have strained since the failed July 2016 coup in Turkey. Now, the most important reasons for the tension is Washington's strong opposition to Turkey's plan to buy S-400 missile system from Russia and Turkish military invasion into northern Syria.

Although Turkish President Recep Tayyip Erdogan's visit to the U.S. on November 13 was intended to resolve the two countries' disputes and open a new horizon in economic and trade relations, differences still remain. 

Though after the meeting at the White House, Trump made some pledges, including increasing trade ties to $100 billion, it takes a long time to fulfill these promises.

Contrary to such pledges, the Pentagon announced that it had replaced all F-35 fighter parts made by Turkey.

While the Turkish and U.S. leaders were meeting, F-35 production program executive Lt. Gen. Eric Fick said at a congressional hearing that Turkey would be completely phased out until March.

At the moment the U.S. has narrowed the number of parts down from 1,000 to 12.

Undersecretary of Defense for Acquisition and Sustainment Ellen Lord affirmed to Rep. Donald Norcross, D-N.J., that as of Wednesday, Turkey’s exit from the program was not expected to cause any F-35 production delays.

The U.S. government believes Ankara's move to buy S-400 missile system from Russia is not in line with NATO policies. Washington also sees Turkey’s decision as a threat to U.S. F-35 fighters. However, Ankara has announced that it will go ahead with its decision to buy the missile system.

Erdogan said it is not a right policy to ask Ankara to deprive itself of the Russian S-400 missile defense system.

Erdogan's remarks came in response to some reports that Trump had requested Turkey to cancel the purchase of S-400 system, a defense system that has been deployed in some parts of Turkey since July 2019.

But after Trump and Erdogan's meeting, the Turkish president claimed that the U.S. president had a positive view on buying the missile system.

Though Trump may seek to strike a deal with Erdogan on the S-400 missile system and F-35 fighter aircraft, based on his own businessmen approach, Ankara's military intervention in northern Syria and its insistence on buying the S-400 system are at odds with Washington. For this reason, the House of Representatives has passed two resolutions against Turkey.

On October 30, the House approved a resolution against Turkey recognizing the Ottoman massacre of Armenians in 1915. 305 representatives voted in favor of the resolution, with only three opposing it. It also passed another resolution calling on Trump to impose sanctions on Turkey over military operations in northern Syria. The resolution was also adopted by 403 votes in favor and 16 against, a move that rose Turkey's anger.

After Erdogan's meeting with Trump, attended by some Congress representatives, senior Republican Senator Lindsey Graham and chairman of the Senate Judiciary Committee vetoed the resolution recognizing the massacre of Armenians by the Ottoman Empire. 

Earlier, Senate Majority Leader Robert Menendez had called for the resolution to be approved. Lindsey Graham noted that he had listened to Erdogan's speech at the White House and criticized a House resolution that recognized the Armenian genocide. 

Menendez argued that "U.S. policy must be unanimous and honest in the face of human rights violations, crimes against humanity, ethnic cleansing, and genocide" and sent it to the Senate for approval.

There is a difference between the White House and Congress in how to deal with Turkey. Also, there is a difference between Republicans and Democrats despite Trump's promises to Erdogan.