President Trump’s surprise decision to suspend sanctions on Russian diesel fuel stunned Ukrainian and European officials, who were meeting with U.S. envoys at an exclusive golf club near Miami.

Russia has reaped a diesel deal and an increase in U.S. pressure on Ukraine as President Trump’s political needs align with his longstanding inclinations toward Russia.

The Republican signatories included former Senate majority leader Mitch McConnell and other senators with decades of experience, putting prominent members of Trump's own party at odds with the preside...