Donald Trump asserts that testimony by witnesses who learned about his scheme to shake down Ukraine from other presidential advisers should be disregarded as “hearsay.” Trump also asserts that John Bolton and other White House officials who were in the room with him are constitutionally “immune” from congressional subpoenas.

By Donald Trump’s standard, the only account our representatives can both trust and hear would be that of Donald Trump, who insists his call with his Ukrainian counterpart was “perfect.”

It’s a claim that will be tested Thursday afternoon when a federal court holds a hearing on Deputy National Security Adviser Charles Kupperman’s lawsuit seeking a ruling on whether he must comply with a congressional subpoena following “the assertion of immunity from congressional process made by the president.” Charles Cooper, Kupperman’s lawyer, is a former Reagan administration official who also represents John Bolton. Also on Thursday, an argument will be held in a separate proceeding brought by Congress to compel former White House Counsel Don McGahn’s testimony in the face of an earlier White House claim of immunity.

As evidenced by torrents of angry tweets, Trump is very frustrated by the damaging evidence testimony Congress has been obtaining in recent days.

Last week, U.S. envoy William Taylor provided Congress with a detailed account of Trump’s and Rudolph Giuliani’s moves to pressure Ukrainian President Volodymyr Zelensky to order investigations of Joe Biden and his son, which Taylor largely learned about from European Union Ambassador Gordon Sondland and others who communicated directly with Trump and others in the White House.

Trump’s defenders immediately dismissed Taylor’s testimony as secondhand. “Did he talk to the president?” Lindsey Graham asked rhetorically. “Oh. That’s hearsay.” In fact, even if the rigorous evidentiary standards applicable in a courtroom proceeding governed Congress’ investigation, Taylor’s account of the admissions of Sondland and others involved in the scheme could well be admissible.

Given Trump’s discounting of “hearsay” accounts, however, one might expect the president to welcome Congress questioning the White House advisers who regularly spoke directly with him, such as Bolton, in order to obtain firsthand accounts of Trump’s “perfect” conduct.

But the opposite has happened. Trump and his defenders have repeatedly demanded the opportunity to question the initial whistleblower, who is legally entitled to anonymity and does not even claim to have firsthand knowledge of the relevant facts. But the White House has doubled down on efforts to prevent White House advisers Trump himself regularly spoke to from being questioned. White House lawyers have ordered White House advisers not to comply with congressional demands for testimony, and the president has invoked a supposed “constitutional immunity” that he claims wholly bars Congress from questioning White House advisers regarding potentially impeachable conduct by the president.

By Trump’s through-the-looking-glass logic, witnesses who work outside the White House should be disregarded, while witnesses who were in the room for Trump’s alleged abuses of power firsthand may not be heard.

Trump’s claim of “constitutional immunity” goes well beyond an assertion of executive privilege, which is qualified, meaning that it can be overcome by a showing of sufficient need. The Supreme Court has ruled that otherwise potentially privileged presidential communications must be disclosed in law-enforcement proceedings if they contain potential evidence of a crime. Congress likewise has a strong argument that a presidential executive-privilege claim must give way during its impeachment inquiry.

By contrast, Trump asserts that a “constitutional immunity” doctrine allows him to prevent senior White House advisers from testifying, even if they are the only competent sources of evidence of grave, and potentially impeachable, presidential misconduct.

Prior presidents have similarly asserted that their most senior advisers cannot be subpoenaed by Congress. The only judicial decision to address the issue, however, concluded that the president’s closest advisers are not categorically immune from congressional subpoenas. That court ruled that George W. Bush’s former White House counsel Harriet Miers had to provide testimony to Congress regarding alleged misconduct in connection with the firing of federal prosecutors. The case, however, was settled before an appeal was heard when the Bush White House accommodated Congress by allowing Miers to testify.

Trump, however, has not demonstrated any inclination to reach accommodations with Congress. To the contrary, White House counsel Pat Cipollone has declared the president’s intent to categorically resist Congress’ impeachment inquiry. Accordingly, it seems all but certain that Trump will press his “constitutional immunity” claim as far as possible, possibly to the Supreme Court.

The White House’s apparent hope is that, if the Supreme Court upholds Trump’s immunity argument against permitting the testimony of close presidential advisers and sufficient numbers of senators accept Graham’s argument for disregarding the “hearsay” testimony of Taylor and others, then Trump could deny Congress critical evidence, thereby effectively rendering himself immune from impeachment and removal. At the very least, ongoing litigation might allow Trump to play for time.

Trump’s plan to starve Congress of critical evidence may fail, however, even if the courts prove to be receptive to the president’s “constitutional immunity” argument. This is because, as reiterated in a recent DOJ Office of Legal Counsel opinion concerning McGahn, it has long been understood that the immunity doctrine applies only to “close” presidential advisers, defined as the most senior officials who assist the president on a daily basis and therefore constitute his alter egos. For this reason, some lower level, but still relatively senior officials, such as former National Security Council Russia expert Fiona Hill and Ukraine expert Alexander Vindman, have complied with congressional subpoenas for their testimony.

And a number of such officials appear to have critical information to share. For example, according to his opening statement, Vindman was among those on the line during Trump’s now infamous call with Ukraine President Zelensky, and has apparently testified before Congress about it. As Vindman’s reported account demonstrates, even if Trump does succeed in preventing, or delaying, the testimony of Bolton and others among the president’s most senior advisers, Congress may nonetheless obtain additional firsthand accounts of Trump’s potentially grave misconduct. If so, Trump’s stonewalling may prove to be for naught.