As usual, the National Review gets it right here. Republicans, driven by the obstinacy of the President, are making arguments that are implausible to embarrassing.
Abuse of power can certainly rise to the level of a high crime and misdemeanor. It can also be a peccadillo. Same as if the President committed a named crime.
Republicans should admit that Trump abused his power, as he clearly did. They should then argue that while an abuse occurred, it does not rise to the level of a high crime and misdemeanor and thus does not merit removal from office.
National Review gets it right and I agree with them. Republicans should admit to Trump’s wrong doing, but acquit him as a peccadillo. Then leave it to the voters to affirm or reject that judgement in November.