(CNN) President Donald Trump offered a reserved rebuttal to Sen. Lindsey Graham's assertion that the administration's response to Iran shooting down an American drone earlier this summer was viewed as "weakness," with the President calling his response "a sign of strength."

Trump's tweet was an unusual rebuke of a strong congressional ally -- though much gentler than some of his previous attacks on critics -- and comes as sources tell CNN that no definitive US response to this past weekend's attacks on Saudi oil fields is expected until Secretary of State Mike Pompeo returns from his trip to Saudi Arabia that begins Tuesday night.

Graham's Twitter thread about the attacks on Saudi oil facilities began Tuesday with praise for Vice President Mike Pence after he briefed Senate Republicans. The attack, claimed by Houthi rebels in Yemen, forced state-owned Saudi Aramco to halve its production, taking more than 5% of the world's daily crude oil consumption off the global market.

Implicating Iran in the attacks, Graham lauded "the Administration's efforts to create a regional coalition, thoroughly brief the Congress on the actions taken, and come up with a plan of action to restore deterrence against an evil regime in Iran."

The South Carolina Republican then directly addressed Trump, writing , "The measured response by President @realDonaldTrump regarding the shooting down of an American drone was clearly seen by the Iranian regime as a sign of weakness."

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