"We need to look at whether or not Hunter Biden corruptly engaged in lobbying. Didask the prosecutor to be fired because he was investigating his son?" Graham asked during an interview on Monday with Fox News's

He added that he hoped Senate Foreign Relations Committee Chairman(R-Idaho) "will open up an investigation about the role of the State Department in all this."

"I believe it would be more appropriate for our committee to wait on examining these matters until after the House completes its process (one way or another)," Risch wrote in the letter, which is dated Oct. 29, but was obtained by The Hill on Tuesday.

"At the appropriate time, we will look into these matters in greater detail in consultation with the Senate Select Committee on Intelligence," Risch added.

Risch— in a letter to Sen.(N.J.), the top Democrat on the Foreign Relations panel—said that he would wait until after the House impeachment inquiry wraps up before digging into delays in Ukraine assistance and a July 25 call at the center of the impeachment inquiry.