A Senator who says "Abuse of Power is not impeachable" is saying that the Constitution grants the president the power to use his office for corrupt purposes.
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(The Constitution includes the emoluments clause for a reason)
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The federal criminal code applies to ordinary citizens.
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The House was smart to stay away from the federal criminal code, which also confuses people into thinking that this is a criminal trial. It is not.
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That's why criminal trials have such a high standard of proof (beyond a reasonable doubt)
The Constitution makes clear that no criminal punishments apply in this trial.
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This is not life, liberty, or property.
Trump's defense wants you to think this is like a criminal trial. It is not. The only thing Trump risks losing is the privilege of being President of the United States.
Nadler pointed out another reason looking to the federal criminal code for impeachable offenses is nonsensical: This requires anticipating, in advance, how a president might abuse his office, and passing a law against it . . .
Also punishment can extend to inability to ever hold office or trust again.
(This is as far as the punishment can go, but doesn't have to go this far)
Expect the defense to argue that the burden of proof must be beyond a reasonable doubt. Nope, sorry.