More Democrats are warning that Trump pulling out a vital treaty would be a 'gift' to Putin

• Four senior Democrats have sent a letter to Secretary of State Mike Pompeo and Secretary of Defense Mark Esper on Tuesday warning against pulling out of the Open Skies treaty.
• The treaty, which 34 countries, including the US and Russia, have signed, requires signatories to give other countries notice 72 hours before flying observational missions over their airspace.
• "This is not a spying operation," Daryl Kimball, the executive director of the Arms Control Association, previously told Insider. "These are observational flights."
• Visit Business Insider's home page for more stories.

Four senior Democratic lawmakers said on Tuesday they believe the Trump administration is considering withdrawing from the Open Skies Treaty, which allows the US, Russia, and other signatories to make unarmed surveillance flights over other signatories' territory, arguing this would benefit Russia and undermine confidence in the US commitment to Ukraine.

"Pulling out of the Open Skies Treaty, an important multilateral arms control agreement, would be yet another gift from the Trump administration to [Russian President Vladimir] Putin," Sen. Robert Menendez, Sen. Jack Reed, Rep. Eliot Engel, and Rep. Adam Smith wrote in a letter to Secretary of State Mike Pompeo and Secretary of Defense Mark Esper.

Menendez is ranking member of the Senate Foreign Relations Committee, and Reed is the ranking member of the Senate Armed Services Committee. Engel and Smith are the chairmen of the House Foreign Relations Committee and Armed Services Committee, respectively.

Engel previously sent a letter to Trump's new national security adviser, Robert O'Brien, expressing concern about such a withdrawal.

"I request your personal engagement on this matter to ensure that the United States does not unwisely and rashly withdraw from the Open Skies Treaty," Engel wrote, saying the treaty "continues to serve" US national security and "is particularly important as a check against further Russian aggression against Ukraine."

'This is not a spying operation'

The Open Skies Treaty was originally signed in 1992 by the US, Russia, and 22 other signatories. The treaty went into force in 2002, and 34 countries have now signed on. It requires signatories to give each other notice 72 hours before flying observational missions over their airspace.

A Russian Tu-154 aircraft made such a flight over Great Falls, Montana, earlier this year, taking aerial photographs.

A State Department spokesman, speaking on condition of anonymity, declined to comment on the letter and told Reuters that the US "continue[s] to implement the treaty and are in full compliance with our obligations under this treaty, unlike Russia."

Some experts and administration officials believe the treaty has outlived its usefulness, partly because of alleged violations by Moscow, including restrictions Moscow imposed on certain observation flights over Kaliningrad, a Russian exclave on the Baltic Sea between Poland and Lithuania, and flights near Russia and Georgia's disputed border.

In response, the US in 2016 restricted Russian observation flights over the Pacific Fleet in Hawaii and missile-defense interceptor sites at Fort Greely in Alaska.

A former Trump administration official, speaking on condition of anonymity, told Reuters the treaty was outdated because the US can share satellite imagery that is not overly sensitive with other countries. The former official also said countries now have access to high-quality commercial satellite photographs.

"This is not a spying operation," Daryl Kimball, the executive director of the Arms Control Association, previously told Insider about the treaty. "These are observational flights. It is a form of monitoring and verification about the military activities and facilities on each side."

Kimball also said that the treaty benefits both Russia and the US and its allies. It helps Russia know more about US military capabilities and allows the US and allies to know about Russian military operations.

"And that transparency reduces uncertainty and the risk of conflict due to worst-case assumptions," Kimball said.

(Reporting for Reuters by Arshad Mohammed; editing by Rosalba O'Brien)

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