Ahead of Trump’s meeting with Putin, three U.S. senators wrote to Trump to express “deep concern” about reports that his administration planned to discuss the return to Russia of diplomatic compounds in Maryland and New York that were seized by the Obama administration last year in response to alleged Russian election meddling.

Republican Senators Johnny Isakson and Marco Rubio and Democratic Senator Jeanne Shaheen said returning the facilities would “embolden” Putin and encourage further efforts by Russia to interfere in Western elections. All three are on the Senate Foreign Relations Committee.

The White House declined to offer details on what Trump would request of Putin and what he might offer in exchange for cooperation.

U.S. Secretary of State Rex Tillerson said Trump wanted to talk about how the two countries can work together to stabilize war-ravaged Syria.

“The United States is prepared to explore the possibility of establishing with Russia joint mechanisms for ensuring stability, including no-fly zones, on-the-ground ceasefire observers, and coordinated delivery of humanitarian assistance,” Tillerson said before leaving the United States to join Trump in Germany.

Trump was also grappling with a response to North Korea’s successful test of an intercontinental ballistic missile, which analysts say had a long enough range to reach Alaska.

Curbing Pyongyang’s nuclear ambitions has been Trump’s most pressing foreign policy priority, and he met with leaders from Japan and South Korea on Thursday evening to discuss it. He is also slated to meet with Chinese President Xi Jinping at the G20.

“I’d like to see the president figure out how to engage Russia on North Korea,” said Representative Francis Rooney, a Republican from Florida who is on the House Foreign Affairs Committee.

“What I suggested to the president here a while back was that since we have all these conflicting issues about Russia right now and we’re still reeling from the fact that they took Crimea, maybe this is an opportunity to reset the Russia relationship in a positive manner,” Rooney said in an interview.