People keep saying that but it has never been tested. Clinton's articles included high crimes.
I could see that if the House passed articles like "obstructing" a non existent crime, the first thing done in the Senate trial will be the equivalent of a motion to dismiss since no "Treason, Bribery, or other high Crimes or Misdemeanors" were presented.
Might be the shortest Impeachment trial in history.
Such a motion would need only a bare majority.