I really liked this Catherine Rampell opinion piece in The Washington Post, If there were ever a red line for Republicans, Trump crossed it Friday. Or not..
We have a president with pronounced authoritarian tendencies, who believes he “alone can fix it”; who signs sweeping executive orders reportedly without even briefing relevant Cabinet members on the logistical, humanitarian and national security consequences; who directs his staff and surrogates to lie about the tiniest and most ridiculous and easily fact-checkable of details; and whose staffers brought us to the brink of a constitutional crisis when they ignored federal court orders.
She goes on to list (with substantiating links) the various GOP principles he's already violated that the GOP Congress has chosen to ignore. I think it's the best summation of the case I've seen so far, though I don't think it's quite impeachable yet; but Trump is moving fast.