WASHINGTON — President Trump is definitely building a wall — but it is between the White House and the House of Representatives.

In the aftermath of Robert S. Mueller III’s report, the White House has quickly assumed a defiant, hard-line stance that it will not respect subpoenas and demands for information from various House committees exploring the president’s conduct and business affairs. It is an extreme position even measured against the reluctance of past administrations to produce potentially damaging witnesses and evidence of executive branch wrongdoing or ineptitude.

Such a blanket refusal has serious implications not only for the relationship between the current Congress and the administration, but also for the future ability of Congress to conduct oversight of any administration, depending on how the intensifying fight plays out.

“It is a radical departure and a radical theory from anything that has been done before,” said Phil Schiliro, a onetime Democratic staff director for the House oversight committee and a former top legislative adviser to President Barack Obama.
After striking an increasingly combative tone following the release of Mr. Mueller’s findings, Mr. Trump proclaimed on Wednesday that the White House would be “fighting all the subpoenas” because he considered them partisan and politically motivated.

“These aren’t, like, impartial people,” the president said.

In an interview on Tuesday with The Washington Post, the president characterized the demands as simply the work of one party, suggesting that was sufficient reason to ignore them even though they represent official requests from the House, not just House Democrats. “I don’t want people testifying to a party, because that is what they’re doing if they do this,” Mr. Trump told The Post.

The Justice Department backed up his stance. It disclosed that Attorney General William P. Barr would prohibit John Gore, a top official in the agency, from appearing Thursday as ordered to discuss any role in adding a citizenship question to the 2020 census despite the fact that he was called under a bipartisan subpoena.

That move came on top of the administration’s position that it did not want Donald F. McGahn II, the former White House counsel, to testify about the Mueller report, as well as its instruction to Carl Kline, the former White House personnel security director, not to appear to answer questions about the issuance of security clearances. The Treasury Department also refused to obey an order from the Ways and Means Committee to produce the president’s tax returns despite a law that gives the panel the authority to obtain the documents.

“This is a massive, unprecedented and growing pattern of obstruction,” said Representative Elijah E. Cummings, Democrat of Maryland and the chairman of the oversight panel. He also warned administration officials to be careful in blindly following the president’s instructions.
“These employees and their personal attorneys should think very carefully about their own legal interests rather than being swept up in the obstruction schemes of the Trump administration,” Mr. Cummings said.
In many past cases, there was a mutual recognition that Congress had substantial legitimate oversight power. Republican and Democratic administrations would reach an accommodation through a negotiation about who would ultimately testify or the extent of documents to be provided.