When you get right down to it, the president really can be impeached only for a serious abuse of power. Everything else is just a specific example of a serious abuse of power and therefore a redundancy. Treason and bribery are both clearly high crimes and therefore are redundancies in being named separately. Treason and bribery are both also abuses of power.
Clinton's gross indiscretion was also an abuse of power, becoming serious when it became a perjury, if not sooner.
Nixon's taped suggestion to use the CIA to block the FBI's investigation into Watergate was also a serious abuse of power, as was his suggestion to raise $1,000,000 to buy silence.
Andrew Johnson was impeached on 11 articles, not only for firing Stanton in violation of the Tenure in Office Act, but separately for sending a letter to Stanton's proposed replacement about it, and separately again in four more articles for conspiring with others about doing it.
Johnson was even impeached in one separate and additional article for uttering "with a loud voice, certain intemperate, inflammatory, and scandalous harangues, and did therein utter loud threats and bitter menaces ... against Congress [and] the laws of the United States duly enacted thereby, amid the cries, jeers and laughter of the multitudes then assembled and within bearing." Sound familiar?
And judges have been impeached for inebriation on the bench. Not a statutory misdemeanor, but certainly a serious abuse of power.
"High crimes and misdemeanors" all come down to serious abuses of power, of one type or another.