The House has sole power over impeachments. Simple majority vote. The difficulty is scheduling it, the leadership controls this. A more likely path is four Republicans could make a declaration to caucus with the Democratic party, and change the leadership. Again, simple majority vote.
The Senate has sole power over impeachment trials. The trial and conviction vote have no quorum requirement. Republicans will have to show up and vote to acquit, explicitly, to protect Trump.
The law is clear, upon conviction the president is removed from power. The only power any person has is the power people voluntarily give to him. He can also throw poop if so inclined, he's plenty full of it.
But if not one thing is yielded to him, if without any violence he is simply not obeyed, he becomes naked and undone and nothing, just as when the root receives no nourishment, the branch withers and dies. - Étienne de La Boétie, Discourse on Voluntary Servitude: Why People Enslave Themselves to Authority
The House of Representatives just needs a majority vote to approve the articles of impeachment, but to convict, the Senate requires a two-thirds vote. That's what I meant by a supermajority. My bad for the miscommunication.
The Senate needs 2/3rds of those present. It is not 2/3rds of the membership. They have to appear if they want to protect him.