"My motive for bringing him to the committee is because of other involvements with whether or not the Foreign Agent Registration Act has been adequately enforced by this administration and by the Obama administration because I think it's been lackadaisical enforcement and he would be an example of that lackadaisical enforcement", Grassley said, as reported by the Des Moines Register.
Sen. Richard Blumenthal, a member of the committee, said it was "long overdue" that Manafort be called to testify.
Paul Manafort already has volunteered to talk to congressional intelligence committees investigating whether there was any collusion between the Trump campaign and the Russian government attempting to interfere in the 2016 presidential election. Yet she was able to meet with Trump Jr.at Trump Tower in June.
According to the Former Russian prosecutor, Natalie Veselnitskaya, she was initially denied a U.S. Visa to enter the county but was later given immigration parole. He said he will leave that to Robert Muller, the special counsel investigating the president's campaign ties to Russian Federation.
Manafort disclosed the meeting in a package of information he provided to the Senate and House intelligence committees, who have been investigating potential coordination between Russian Federation and the Trump campaign, as is Robert Mueller, the former Federal Bureau of Investigation director appointed by the Justice Department as the special counsel.
A lawyer for Donald Trump Jr. did not immediately respond to a message seeking comment on whether his client would agree to appear before the committee. He said he was willing to subpoena him if he refused to testify.
Trump Jr. told the intermediary, a music publicist named Rob Goldstone, of the offer: "I love it".
'But the real way I feel comfortable inviting him is ever since President Trump was elected it seems like every conversation that has come from somebody in the family, where there's been some sort of issue, they've seemed always to be very, very open, ' Grassley said.
Tuesday morning, Trump Jr. posted an email chain on his Twitter account documenting the arrangement.
Trump says the woman is a private attorney who has "roamed the hallways" of the U.S. Congress.
He said the president had not been aware of Trump Jr.'s June 2016 meeting and didn't find out about his son's email exchange until "very recently".
"In retrospect I probably would have done things a little differently", Trump Jr. said.