SCOTUS was NEVER granted the powers they have claimed by the Constitution. They CAN be stopped!

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3. Congress *could* do far more than change the number of justices.

Unlike their original jurisdiction, control of SCOTUS' appellate jurisdiction is left to Congress, which they've done in the various judiciary acts.

But the chances of Congress changing the Court's appellate jurisdiction or otherwise substantially restricting SCOTUS in the forseeable future is approximately zero.