(CNN) Sen. Mark Warner, the Senate Intelligence Committee's top Democrat, told CNN's Manu Raju Thursday that President Donald Trump "should withdraw" his pick to be attorney general, William "Bill" Barr, because of a memo Barr sent to the Department of Justice this summer weighing in on the special counsel investigation.

"I think the President should withdraw this nomination," said Warner. "It appears that the number one qualification Trump is looking for in an AG is someone that will try to undermine the Mueller investigation."

Warner said that "in effect" Barr's memo was "an attempt to solicit" the nomination, while the special counsel probes whether the President obstructed justice during the investigation of Russian interference in the 2016 campaign. He called the memo "almost tacky" and "at the very least unseemly."

In June 2018, Barr sent a memo to senior Department of Justice officials, reaching a decisive and controversial conclusion that Trump's interactions with ex-FBI Director James Comey would not constitute obstruction of justice. Trump is expected to formally nominate Barr, who held the position during George H.W. Bush's presidency, next month.

Democrats have objected to the fact that Barr weighed in on such a sensitive issue that he would be poised to oversee. Barr discussed the memo with Trump and told him it would likely come up during his Senate confirmation, a source familiar with the discussions told CNN.

Read More