Rep. Adam Schiff (D-CA), the ranking member on the House Intelligence Committee, told the Washington Post on Friday that Republicans on the committee blocked an effort by Democrats to learn more about a phone call Donald Trump Jr. made that may have been related to the June 2016 Trump Tower meeting with a Kremlin-linked lawyer.

Trump Jr. made three phone calls on June 6, 2016, three days before the meeting, two of which were with Emin Agalarov, the Russian pop star who helped arrange the Trump Tower meeting, according to Democrats’ official response to the Republican report from the House Intelligence Committee released on Friday. In between the two phone calls, Trump Jr. spoke with someone using a blocked phone number, which may have been his dad, Donald Trump, according to the Democrats.

Democrats wanted to subpoena the phone records to determine the identity of that person, but Republicans refused, Schiff told the Washington Post.

“We sought to determine whether that number belonged to the president, because we also ascertained that then-candidate Trump used a blocked number,” Schiff told the Post. “That would tell us whether Don Jr. sought his father’s permission to take the meeting, and [whether] that was the purpose of that call.”

“We asked Republicans to subpoena the records and they refused. They didn’t want to know whether he had informed his father and sought his permission to take that meeting with the Russians,” he added.

President Donald Trump has denied that he was aware of the meeting between Trump Jr., other campaign officials, and a Kremlin-linked promising damaging information on Hillary Clinton.

Read the full Washington Post report here.