President Trump's deal to buy diesel fuel from Russia and angry outbursts about Ukraine's President Zelenskyy are raising concerns on Capitol Hill.  A number of lawmakers on both sides of the aisle are questioning the president's support for Ukraine and are even calling for an investigation.

Ukraine launched one of the biggest aerial attacks to date, with more than 1,000 drones sent against Russian targets, including oil export terminals and an oil depot. The strikes come as the rift between President Trump and President Zelenskyy is growing.  

Trump suggested Ukrainians should elect a new president. "I think I find Zelenskyy to be more difficult to deal with than Putin," he said.

Last week President Trump negotiated a deal with Russia to buy millions of tons of diesel fuel in an attempt to bring down gas prices in the U.S.  He essentially put on hold a sanctions bill crafted by the late Sen. Lindsey Graham and supported by 86 senators. That's led to charges that he's giving a boost to Vladimir Putin's war machine.

"Personally, I would choose to keep the pressure on Russia to end the war and get the gas prices down," said South Carolina Sen. Darline Graham, "because I don't trust Putin and don't trust Russia."

Meanwhile, Starlink, a U.S.-provided internet service critical to Ukraine's war effort, was partially disabled. President Zelenskyy said he believes it was a message from the U.S. government. Secretary of State Marco Rubio disagrees.

"I'm not sure Zelenskyy knows what he's talking about, but it wasn't deliberate. We have nothing to do with that," Rubio said, adding that Starlink is now fully restored. However, Zelenskyy says the service is reduced and less effective.

"No, no, of course we have limitation," he said. "The speed is maximum 161 kilometers. Not miles, kilometers."

Ohio Republican Congressman Mike Turner wants answers. "There needs to be an investigation, needs to be a congressional investigation," Turner said Sunday on CBS's Face the Nation.

He said this isn't the first time U.S.-provided military help to Ukraine has gone awry and later blamed on unnamed Pentagon employees.  There have also been claims of lapsed intelligence reports.

"Lives are at risk and lives are lost over these things," he said.

Zelenskyy warned the U.S. not to side with Russia. "If United States will support Putin, I mean, it's unbelievable. It's a tragedy. It's a historic mistake and a big tragedy," he said.

President Trump says one goal is to keep Russia from giving more support to Iran in its conflict with the U.S.