Who says a law must be involved, from the wiki on high crimes and misdemeanors:
The charge of high crimes and misdemeanors covers allegations of misconduct by officials, such as perjury of oath, abuse of authority, bribery, intimidation, misuse of assets, failure to supervise, dereliction of duty, unbecoming conduct, refusal to obey a lawful order, chronic intoxication, and tax evasion.
Abuse of authority would certainly fit. What set it off was the refusal to send the whistleblower report per the law, which is refusal to obey a lawful order. If the whistleblower report had been sent to congress, I doubt we would be here today.