WASHINGTON — When President Donald Trump’s former campaign manager, Corey Lewandowski, appeared in January before the House intelligence committee investigating Russian political interference, he refused to answer questions about his conversations with Trump after he was fired by the future president in June 2016.

The Republicans running the panel did not respond with a subpoena, which Congress can use to compel testimony. They instead invited Lewandowski to return when he was ready, and he’s scheduled to testify again Thursday.

Steve Bannon, the former White House chief strategist, Donald Trump Jr., the president’s eldest son, and Hope Hicks, the outgoing communications director, also have declined to discuss certain topics in closed-door House committee hearings.

Over in the Senate, top Trump administration intelligence and law enforcement officials, most notably Attorney General Jeff Sessions, have refused to discuss their private conversations with Trump, at least in public hearings, regarding Russia and other issues.

Most of the conflicts over congressional testimony have revolved around executive privilege, the president’s legal authority to keep some conversations and other material secret to protect internal deliberations. Although the White House hasn’t formally invoked the privilege, Trump’s current and former aides said they would not answer questions to protect the president’s right to cite the privilege later should he seek to do so.

Legal experts said the White House has broadened the traditional use of executive privilege to direct individuals to avoid answering questions about conversations with the president.

The Trump White House is “preventing any testimony from people on the grounds that something, at some point, is potentially covered by executive privilege,” said Mark Rozell, a professor at George Mason University who has studied the presidency.

Jim Schultz, a former deputy counsel in Trump’s White House who now works at the Cozen O’Connor law firm, said there’s nothing wrong with safeguarding the president’s prerogative to keep some information secret.

‘It’s the obligation of the White House counsel to protect the institution of the White House and the executive privilege that goes along with it,” Schultz said.

Rep. Jerrold Nadler, the top Democrat on the House Judiciary Committee, conceded that partisanship can be at play. But he said Republicans are bending over backward to accede to White House efforts to rope off areas of inquiry

“I’ve rarely seen a total surrender, a total failure of congressional oversight,” Nadler said. “They’re going further than the president’s party usually goes.”

Republicans have accused Democrats of conducting a partisan quest to embarrass Trump and his inner circle. They also have argued that special counsel Robert Mueller is conducting a criminal investigation of the Russian meddling, and whether Trump or his aides committed any crimes, reducing pressure on Congress to find the answers for themselves.

The venue for most conflicts involving the Russia investigation has been the House intelligence committee, one of three congressional panels conducting inquiries.

When the House panel interviewed Donald Trump Jr. about his June 2016 meeting at Trump Tower with a Kremlin-linked lawyer, he refused to recount his conversation with his father about the meeting, claiming attorney-client privilege because a lawyer was present at the time.

Bannon, the former White House strategist, rejected any questions from the committee regarding events or conversations after the election. After the committee slapped him with a subpoena, Bannon agreed to return for another hearing.

But during his second appearance, he was only willing to address a predetermined list of yes-or- no questions that White House lawyers had helped him prepare.

A spokeswoman for House Speaker Paul Ryan, R-Wis., declined to discuss whether Bannon would be held in contempt.

A spokesman for Rep. Devin Nunes, the panel’s chairman, did not respond to a question about how many subpoenas have been issued in the investigation.

Rozell said the Constitution’s separation of powers is no longer working as envisioned.

“James Madison would not be happy to see this. He believed each branch of government would zealously defend its prerogatives,” he said.

chris.megerian@latimes.com