Scott, impeachment is both political and legal. If it has to lean one way or the other, I'd say it leans political. Here's why.
In their book on impeachment, @tribelaw and @JoshuaMatz8 explain that the drafters of the Constitution specifically decided . . .
. . . NOT to give the powers of impeachment and removal to the judicial branch.
What's good about this decision is that it prevents the president from being able to appoint the people who would decide his guilt.
2/ Giving the authority to Congress also transforms a legal process into a political process.
Those who acts as judge and jury of the president are elected officials.
They answer to constituents, and those constituents are basically all Americans.
3/ Thus the advantage of Congress deciding is that the judges & jurors are not appointed by the president. The disadvantage is that the process becomes political. You can expect a Senate trial to contain much grandstanding. The Court of Public Opinion takes on greater importance.
4/ I've argued that is partly why Trump isn’t worried about whether his defense has legal merit.
Trump expects, ultimately, to be tried in the Court of Public Opinion, which is where he is comfortable. He doesn’t inhabit the world of facts. He enacts political theater.
(Remember: Impeachment doesn't mean removal. The Senate removes with a 2/3 vote.)
The Constitution requires the Chief Justice to preside over the Senate trial, which (I assume) was intended to contain some of the political theater and inject actual law.
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