President Donald Trump publicly demanded that Ukrainian President Volodymyr Zelensky stop striking Russian oil refineries over its impact on diesel prices, a central aspect of Ukraine’s drone campaign against Russia.

The latest energy issue to emerge has been a spike in diesel oil prices, something that could further jeopardize Republican chances in the midterm elections. On Sunday, Trump said he had spoken with Zelensky to demand he stop Ukrainian strikes on oil refineries, given the impact on diesel oil prices, which hit a nationwide average of $6 per gallon for the first time in U.S. history on Friday.