Congress Russia Probe McGahn (copy)

A name placard is displayed for former White House Counsel Don McGahn, who did not appear before a House Judiciary Committee hearing Tuesday on Capitol Hill in Washington. (AP Photo/Patrick Semansky)

You practically need a scorecard to keep up with all the conflicts between Congress and President Donald Trump over executive privilege. At last count, a federal district court has required Trump’s accountants to pass along documents connected to his taxes. Meanwhile, the administration is withholding the returns themselves on the basis of a claim of privilege. And Trump has directed former White House counsel Donald McGahn not to respond to a House subpoena requiring him to testify about episodes he described to special counsel Robert Mueller’s investigation.

Fortunately, there’s a handy-dandy principle you can rely upon to determine when Congress should win and when the president should.

It’s this: Congress should get the information it needs to do its job of legislation and oversight, and the president should be able to withhold what is necessary for him to do his job well.

If you prefer prediction to principled explanation, it’s a safe bet that the lower courts will follow this principle. (The U.S. Supreme Court is something else again.)

In practice, that means Congress can get the records from Trump’s accountant — because it has legislative oversight over presidential finances and even potential impeachment. The same goes for Trump’s tax returns, which Congress is entitled to by federal law.

But McGahn shouldn’t and can’t be compelled to appear before Congress, because the president needs to be able to keep confidential his conversations with his senior advisers in order to run the country effectively.

For what it’s worth, I didn’t invent this principle. The Supreme Court did, in the landmark 1974 decision of United States v. Nixon. Writing for a unanimous court, Chief Justice Warren Burger held:

“A President and those who assist him must be free to explore alternatives in the process of shaping policies and making decisions, and to do so in a way many would be unwilling to express except privately.”

Burger’s basic idea here is twofold. First, as a pragmatic matter, the president can’t do his job unless he gets the freely expressed, unfettered advice from his senior aides. If those advisers know that they could be subpoenaed and required to testify under oath about what they’ve told the president, either by a court or by Congress, they will be constrained in their willingness to express themselves fully and freely.

The second element of Burger’s logic is constitutional. The pragmatic requirement to let the president function effectively can be grounded in the Constitution. It’s not in any specific clause, to be sure. Rather, the separation of powers between the different branches of government can be construed to protect each branch’s ability to do its own job.

The president’s need to get good advice from his advisers certainly extends to the White House counsel. Almost no presidential adviser is more central.

The strongest argument for forcing McGahn to testify is that Trump already waived executive privilege by allowing McGahn to speak to Mueller. But the Trump administration has a non-crazy response to that argument: It is different to let one executive employee speak to another member of the executive branch (which Mueller is, as part of the Justice Department) than it is to let the former White House counsel be subpoenaed by a separate branch of government.

Trump isn’t wrong to say that if McGahn can be subpoenaed, that could create a precedent for future White House counsels. On balance, the principle of executive privilege should likely be read to stop Congress from subpoenaing McGahn.

Yet it’s important to notice that Burger’s formulation doesn’t unduly elevate the president’s interests above those of Congress or the courts.

Similarly, Congress has the well-established authority to subpoena materials that fall within its legitimate exercise of legislative authority under the Constitution.

The principle of executive privilege isn’t perfect by any means. The Supreme Court could also change it. But it’s worked all right for 45 years — and it’s worth applying it now.

Noah Feldman is a Bloomberg Opinion columnist.

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