Biden raises missile purchase with Turkey's Erdoğan

The backdrop: In 2019, Turkey received "the first group of equipment" from a Russian S-400 air defense system despite warnings from the U.S., which said the system could compromise the alliance's security.

• Erdoğan has said he may purchase a second Russian missile system, adding that "nobody can get involved with this."
• Erdoğan last week walked back a threat to expel U.S. Ambassador David Satterfield and nine other foreign envoys after they called for the release of a jailed philanthropist.

What they're saying: "I think obviously the S400 is an issue that continues to be a concern for Congress and continues to be a factor in all of these broader issues as part of our defense relationship," a senior administration official told reporters.

• "I mean, the President and the administration have long been clear that the S400s are a problem."

Worth noting: The White House said Biden and Erdogan also discussed human rights violations and regional issues in Afghanistan and Syria, among other topics.