President Donald Trump is criticizing Ukrainian President Volodymyr Zelensky amid a US-Russia diesel deal, saying that the country’s war with Russia began due to “incompetence” and suggesting that it get a new leader.

Last week, President Trump sided with Russia in this all-important battle when he announced a deal to buy Russian diesel fuel, undercutting U.S. sanctions.

“It is increasingly evident that Russia is unwilling to accept an energy ceasefire proposed by the United States and intends to continue its terrorist air attacks against our people and communities. T...