(CNN) Rep. Adam Schiff of California, the ranking Democrat on the House Intelligence Committee, said Monday that the House panel needs to interview former Trump campaign aide Sam Nunberg as part of its Russia investigation.

Schiff said Nunberg's assertion that President Donald Trump may have known about the 2016 Trump Tower meeting before it occurred is an area that the committee needs to explore.

The congressman called on Nunberg to testify following his declaration in numerous television interviews Monday that he would refuse to comply with a subpoena from special counsel Robert Mueller. Among other comments Monday, Nunberg suggested that Trump may have known beforehand about the June 2016 meeting between Donald Trump Jr., Jared Kushner, Paul Manafort and a Russian lawyer.

"Certainly if Mr. Nunberg has light to shed about what the President knew about the Trump Tower meeting, we would like to find out," Schiff said.

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