WASHINGTON — President Donald Trump on Tuesday said he is opposed to current and former White House aides providing testimony to congressional panels in the wake of the special counsel report, intensifying a power struggle between his administration and House Democrats.

In an interview with the Washington Post, Trump said that complying with congressional requests was unnecessary after the White House cooperated with special counsel Robert Mueller’s probe of Russian interference and the president’s own conduct in office.

"There is no reason to go any further, and especially in Congress where it's very partisan — obviously very partisan," Trump said.

Trump's comments came as the White House made it clear that it plans to broadly defy requests for information from Capitol Hill, moving the two branches of government closer to a constitutional collision.

On Tuesday, two White House officials said the administration plans to fight a subpoena issued by the House Judiciary Committee for former White House counsel Donald McGahn by asserting executive privilege over his testimony.

Separately, the administration directed a former White House official not to comply with a subpoena from the House Oversight Committee, prompting the panel to move to hold him in contempt of Congress. And the Treasury Department defied a second demand from House Democrats to turn over six years of President Trump's tax returns.

Taken together, the moves mark a dramatic escalation of tensions between the president and congressional Democrats — deepening a fight that may ultimately be resolved only by a protracted court battle.

House Speaker Nancy Pelosi (D., Calif.) said Tuesday the findings of the Mueller report, the investigations by congressional committees, and the White House response had created a pivotal “moment in our history.”

"Now we see the administration engaging in stonewalling of the facts coming to the American people," Pelosi said in an interview for the Time 100 Summit in New York.

White House lawyers plan to tell attorneys for administration witnesses called by the House that they will be asserting executive privilege over their testimony, according to two officials familiar with internal plans who, like others interviewed for this story, spoke on the condition of anonymity.

In his interview with the Post, Trump maintained that the White House Counsel’s Office has not “made a final, final decision” about whether it will formally assert executive privilege and try to block congressional testimony. But he said he opposes cooperation with House Democrats, who he claimed are trying to score political points against him.

"I don't want people testifying to a party, because that is what they're doing if they do this," Trump said.

The president said Democrats should be satisfied with what McGahn and other officials told Mueller, calling his decision to allow them to meet with federal investigators an act of transparency that made further congressional cooperation unreasonable.

"I allowed my lawyers and all the people to go and testify to Mueller — and you know how I feel about that whole group of people that did the Mueller report," Trump said. "I was so transparent; they testified for so many hours. They have all of that information that's been given."

"I fully understood that at the beginning. I had my choice," Trump added of his decision to allow his aides to testify as part of Mueller's probe. "I could have taken the absolute opposite route."

Legal experts said that a White House effort to assert executive privilege over possible testimony by McGahn and other former and current aides who spoke to the special counsel will face legal challenges.

"It seems to me executive privilege was waived when McGahn was permitted to give testimony and to be interviewed by special counsel Mueller," said former Watergate prosecutor Richard Ben-Veniste. "I don't see how the White House can assert executive privilege with something that has already been revealed. To use the Watergate expression, 'You can't put the toothpaste back in the tube.'"

House Judiciary Committee Chairman Jerrold Nadler (D., N.Y.) said Tuesday that the panel is specifically seeking McGahn’s testimony related to subjects described in Mueller’s report, which is now public in a redacted form.

"As such, the moment for the White House to assert some privilege to prevent this testimony from being heard has long since passed," Nadler said in a statement.

McGahn was mentioned more than 150 times in Mueller's report and told investigators about how the president pressured him to oust the special counsel and then pushed him to publicly deny the episode.

Public testimony by McGahn could create a spectacle that would parallel the June 1973 testimony of President Richard Nixon’s former White House counsel, John Dean, whose live televised appearance before a Senate committee painted a vivid portrait for the country of the White House cover-up of the Watergate burglary.

McGahn's lawyer, William Burck, began discussions with the Judiciary Committee about his potential testimony after the panel issued a subpoena Monday, according to people familiar with the matter.

People close to McGahn, who were not authorized to speak publicly, said McGahn is "following the process" and working with the White House on his next steps, despite Trump's public and private anger about his former counsel's prominence in the Mueller report.

"He's not eager to testify. He's not reluctant. He got a subpoena. It compels him to testify. But there are some countervailing legal reasons that might prevent that," said one person close to McGahn, who spoke on the condition of anonymity to describe private discussions. "He doesn't want to be in contempt of Congress, nor does he want to be in contempt of his ethical obligations and legal obligations as a former White House official."

Meanwhile, the House Oversight Committee moved Tuesday to hold former White House personnel security director Carl Kline in contempt of Congress for failing to appear at a hearing investigating alleged lapses in White House security clearance procedures.

The panel subpoenaed Kline following testimony from a White House whistle-blower, Tricia Newbold, who alleged that the White House recklessly granted security clearances to individuals — including presidential son-in-law Jared Kushner — over the objections of career staff.

Newbold, who processed security clearances under Kline at the White House for the first two years of the administration, told the panel that more than two dozen recommended denials for security clearances had been overturned during the Trump administration. She said that Congress was her "last hope" for addressing what she considered to be improper conduct that left the nation's secrets exposed.

White House deputy counsel Michael Purpura wrote a letter Monday instructing Kline, who now works at the Defense Department, not to show up for a scheduled deposition before the committee Tuesday.

In a letter to Kline’s lawyer obtained by the Post, Purpura wrote that a committee subpoena asking Kline to appear “unconstitutionally encroaches on fundamental executive branch interests.”

White House aides said the administration will seek to block Kline from giving any testimony and to prevent other administration officials from speaking to the panel about security clearances.

In a separate letter Monday, Kline's attorney, Robert Driscoll, told the panel that his client would adhere to the White House recommendation.

"With two masters from two equal branches of government, we will follow the instructions of the one that employs him," Driscoll wrote.

In response, Rep. Elijah Cummings (D., Md.), chairman of the Oversight Committee, said he would consult with the House counsel and members of the panel about scheduling a vote to hold Kline in contempt of Congress.

"The White House and Mr. Kline now stand in open defiance of a duly authorized congressional subpoena with no assertion of any privilege of any kind by President Trump," Cummings said in a statement. "Based on these actions, it appears that the President believes that the Constitution does not apply to his White House, that he may order officials at will to violate their legal obligations, and that he may obstruct attempts by Congress to conduct oversight."

On Tuesday, Driscoll said that he and his client "take seriously" both the committee's concerns and the direction of the White House.

"We will continue to review the proceedings and make the best judgments we can," he said.

House Democratic legal advisers have been poring over past congressional subpoena litigation as a guide as they map out a strategy to enforce a contempt citation without the backing of the Justice Department.

In that case, the House would be forced to use civil litigation.

A similar dynamic played out during the Obama administration, when then-Attorney General Eric Holder Jr. faced a subpoena and a contempt resolution from the House Oversight Committee, which was seeking information about a controversial border law enforcement program called Fast and Furious.

The effort to secure information from Holder began in 2011 but was not fully resolved until 2016, long after he left office.

A person close to Pelosi said she fully supports the efforts of her committee chairs to ensure House investigators secure the information lawmakers believe they need to hold the White House accountable.

Efforts to block Congress have also extended to Trump's finances. On Monday, the Trump Organization filed a lawsuit to prevent an accounting firm from complying with a committee subpoena for eight years' worth of Trump's financial records.

And Treasury Secretary Steven Mnuchin on Tuesday told a key lawmaker he would make a final decision as to whether to furnish Trump's tax returns by May 6, committing for the first time to a specific deadline in what has become a major power struggle.

In a 10-page letter to House Ways and Means Committee Chairman Richard Neal (D., Mass.) Mnuchin said the Democrats’ request for Trump’s tax returns raised constitutional and privacy issues that needed to be resolved by the Justice Department before he could make a decision on how to proceed.

The administration is continuing to work on a legal rationale for not turning over Trump's taxes, White House aides said.

The Washington Post’s Rachael Bade, Damian Paletta, and Erica Werner contributed to this article.