Looming over all of this is an ideological battle over the “unitary executive,” the theory that all executive power in the United States government must be vested in the president, and over the legacy of the late Justice Antonin Scalia.
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To understand why this case inspires such intense feelings, turn back the clock about three decades to the Supreme Court’s 1988 decision in Morrison v. Olson. Morrison involved a federal law, which expired in 1999, that provided for “independent counsels” — a form of special prosecutor that could only be fired by the president for cause.

The Supreme Court upheld the independent prosecutor statute by a lopsided 7 to 1 vote, with Justice Antonin Scalia providing the sole dissenting vote.

The thrust of Scalia’s opinion: The Constitution provides that “the executive Power shall be vested in a President of the United States.” For Scalia, “this does not mean some of the executive power, but all of the executive power.” And because the power to bring prosecutions is invested in the executive branch of government, there cannot be a prosecutor who is neither answerable to the president or answerable to some lower official who is answerable to the president.

This is the theory of the unitary executive. The executive branch has a single org chart. And the president must be above everyone else in that chart.
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If a majority of the Court embraced the full implications of Scalia’s dissent, the president could potentially gain the power to fire FCC Commissioners or destroy the independence of the Federal Reserve.

The relative obscurity of the unitary theory, combined with its profound and perverse power claims, has come back into focus during the Trump presidency. For example, just as Bush administration lawyers argued unsuccessfully in court in challenges to some of its key actions, Trump lawyers have argued on behalf of Trump’s immigration policies, claiming that the courts had no right to decide such matters because they are solely within the president’s unitary powers. It turns out that judges of all ideological stripes disagree, so such claims have generally been rejected to date. But with the recent appointment of Federalist Society-vetted judges to the federal courts and the Supreme Court, it is likely such claims will find greater favor in the future.