In this case, he said, current and former Trump aides have declined "to answer questions on the grounds that they were instructed not to do so. This is not standard practice in dealing with unwanted congressional inquiries, and there is no constitutional basis for it."
Jim Schultz, a former deputy counsel in Trump's White House who now works at the Cozen O'Connor law firm, said there was 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.
"If there were another party in the White House, the Democrats would not be thumping away about it," he added.
Rep. Jerrold Nadler of New York, the top Democrat on the House Judiciary Committee, conceded that partisanship could be at play. But he said Republicans were 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."
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Republicans have accused Democrats of conducting a partisan quest to embarrass the president and his inner circle. They also have argued that special counsel Robert S. Mueller III 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.
Still, the pushback is a sharp contrast with how Republicans investigated allegations of wrongdoing in the Obama administration.
As chairman of the House Oversight Committee, Rep. Darrell Issa of California issued more than 100 subpoenas to investigate the failed "Fast and Furious" gun-tracking operation, the Internal Revenue Service's treatment of conservative groups, and armed attacks on a U.S. diplomatic mission and CIA post in Benghazi, Libya.
Issa also successfully pushed to hold then-Attorney General Eric H. Holder Jr. in contempt of Congress after the Obama administration invoked executive privilege to withhold information from his committee. The Justice Department declined to prosecute Holder, who headed the department, a reminder that the executive branch often has more leverage in disputes with Congress.