U.S. Sen. Marco Rubio hammered former ExxonMobil CEO Rex Tillerson during a Wednesday morning confirmation hearing with a steady, hard line of questioning about Russian aggression.

Tillerson’s ties to Russian President Vladimir Putin have been a major point of contention since President-elect Donald Trump picked the longtime oilman to be his secretary of state. The U.S. government has accused Moscow of conducting a multifaceted campaign against U.S. institutions to undermine the democratic process.

Trump has declined to condemn Putin and has even praised him — much to the disappointment of many national security hawks on both sides of the proverbial aisle. The nomination of Tillerson, who was personally awarded the Order of Friendship by Putin, as secretary of state only strengthened this concern.

During the hearing, Rubio interrogated Tillerson over Putin’s alleged interference with the U.S. presidential election and the Kremlin’s military aggression in Syria, Ukraine, Chechnya and elsewhere. A simple yet pointed question about Putin perhaps best illustrated Rubio’s firm and aggressive attack-style approach.

“Is Vladimir Putin a war criminal?” Rubio asked.

“I would not use that term,” Tillerson replied.

“Well, let me describe the situation in Aleppo and perhaps that will help you reach that conclusion,” Rubio said.

Rubio detailed how Putin directed the Russian military to conduct a “devastating campaign” that has targeted schools, markets and other civilian infrastructure — killing thousands in the Syrian city.

Rex Tillerson and Senator Marco Rubio at Tillerson’s confirmation hearing for secretary of state in January in Washington, D.C. (Photos: Joe Raedle/Getty Images, /Joshua Roberts/Reuters)

As Rubio noted, this is not the first time Putin has been involved in these sorts of campaigns. After Putin was first appointed prime minister, in response to a series of bombings, he directed the Russian air force to bomb civilians in Grozny, the capital city of the Chechen Republic (a federal subject of Russia). He recalled how Putin used scud missiles, cluster munitions and thermobaric weapons like fuel-air explosive bombs that burn the air people breathe.

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“He used battlefield weapons against civilians, and when it was all said and done, an estimated 300,000 civilians were killed and the city was completely destroyed,” Rubio said.

Rubio, a former Republican presidential candidate who ran against Trump, said there’s a credible body of reporting indicating that the bombing campaign was part of a “black flag operation” by the Federal Security Service, Russia’s top security agency and the KGB’s primary successor.

“So, based on all this information and what’s publicly in the record about what’s happened in Aleppo and the Russian military, you are still not prepared to say that Vladimir Putin has violated the rules of war and has conducted war crimes in Aleppo?”

Tillerson still would not go as far as Rubio on the issue.

“Now those are very, very serious charges to make and I would want to have much more information before reaching a conclusion,” he replied. “I understand there’s a body of record in the public domain. I’m sure there’s a body of record in the classified domain. And I think in order to deal with a serious question like this —”

Rubio interjected: “Mr. Tillerson, what’s happened in Aleppo is in the public domain. The videos and the pictures are there.”

“I would want to be fully informed before advising the president,” Tillerson concluded.

Tillerson largely danced around Rubio’s repeated questions, but the lawmaker kept pressing him for answers, eventually getting him to admit that it’s “a fair assessment” to say Putin was behind the recent campaign of propaganda and misinformation against the United States.

U.S. Sens. John McCain, R-Ariz., and Lindsey O. Graham, R-S.C., have also been vocal critics of Tillerson’s nomination, citing his ties to Russia.

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