In effect, Washington would be sending weapons to be used against Russian forces at a time when the Kremlin is increasingly hostile to the West and has shown it is ready to escalate a showdown.

There is no guarantee that funneling sophisticated U.S. armaments into the conflict could be decisive, and the gambit could antagonize Vladimir Putin, Russia’s increasingly isolated and hard-to-read leader. In a sign of possible administration push back against Carter’s remarks, the top NATO general Philip Breedlove told the Associated Press in an interview on Thursday that arming Ukraine could spark a “more strident” reaction from Russia.

White House spokesman Josh Earnest meanwhile offered what appeared to be a rebuke of Carter on Wednesday, saying “a decision like this will be made by the Commander-in-Chief,” in a reminder of where power over national security lies in this administration.

The United States also wants to avoid a complete breakdown in ties and a return to the great power competition of the Soviet era, partly because it needs Russian help on key strategic issues, including nuclear talks with Iran, the chaos in the Middle East and in Afghanistan.