In one of the most damning and memorable exchanges of William Barr’s testimony before the Senate Judiciary Committee Wednesday, Sen. Kamala Harris (D-Calif.) asked the attorney general whether President Donald Trump has suggested that he investigate anyone. Barr, fumbling over his words, claimed that he did not know.

As it turns out, Trump has publicly called on the Department of Justice, since Barr took control, to open an investigation into his former political opponent Hillary Clinton and also a potential future opponent: former Vice President Joe Biden.

Trump suggested to Fox News’ Sean Hannity last week that Barr should open an investigation into whether Clinton’s campaign received help from the Ukrainian government during the 2016 election based on information allegedly gathered by the top Ukrainian prosecutor. The president’s desired investigation could also ensnare Biden through the former vice president’s son Hunter Biden’s business with a Ukrainian oligarch, according to The New York Times.

Hunter Biden, a former U.S. lobbyist and international corporate consultant, was hired by Burisma Holdings, a Ukrainian energy company, and placed on the company’s board in 2014. The head of Burisma fled the country after President Viktor Yanukovich was deposed in the Maidan revolution later that year and the company’s business practices came under investigation by prosecutor general Viktor Shokin.

But Western European nations, transnational economic organizations and the United States sought Shokin’s removal. They argued that Shokin was letting corruption slide in the new, post-Yanukovich Ukraine. Shokin did open some corruption investigations, but only into former Yanukovich-connected elites ― including Burisma Holdings.

As part of the West’s campaign to remove Shokin, Vice President Biden visited Ukraine and said corruption was eating the country “like a cancer.” The International Monetary Fund threatened to cut off aid unless it took action on corruption. Ukraine’s parliament voted Shokin out of office. And with it went the investigation into Burisma.

The Bidens have claimed that they never discussed Hunter’s work for Burisma and the effort to remove Shokin did not originate from the vice president, according to the report by The New York Times.

But the new Ukrainian prosecutor general recently reopened the investigation into Burisma. And Trump’s allies are seeking to publicize the issue and foment an investigation in the U.S. This effort is led by Rudy Giuliani, one of the president’s lawyers.

“I would imagine [Barr] would want to see” the results of the Ukrainian investigation, Trump told Hannity on April 26. I would certainly defer to the attorney general, and we’ll see what he says about it,” he added.

Harris’ question to Barr about whether the president “suggested” he open an investigation into anyone was clearly pegged to Trump’s public pursuit of an investigation that would touch both Clinton and Biden. When Barr got stuck on the word “suggest,” he could have been trying to figure out how to describe the president’s indirect suggestion transmitted through a television program.

This is not the first time Trump has sought to abuse his power and get the Department of Justice to investigate his political opponents for his own political benefit. He previously asked ex-attorney general Jeff Sessions to investigate Clinton and has publicly called for investigations of Democrats, including for treason.

President Richard Nixon faced impeachment for ordering the IRS and the security state to target his political opponents.