Trump could be impeached tomorrow, but it would have nothing to do with his (thus far executed) executive orders. It would be due to his failure to divest himself of his businesses, and the extent to which Trump has already used the office of the presidency for economic self-gain.
The long answer to your question is that the conduct leading to an impeachment should be the breach of a law - and not be an insignificant breach, but a large one. "High Crimes and misdemeanors," as the language says.
The short answer to your question is that, in the present era, a politically motivated impeachment can be for whatever Congress wants it to be. We saw that with the baseless letters of impeachment against Bill Clinton.
The Republican-led Congress currently holds all the cards, as far as a Trump impeachment, because they are the majority party. He knows this, and it's why he's going to constantly throw bones to Congressional republicans, even though he parts way ideologically with them on some important issues. The Republicans have a sitting VP whom they'd much rather have in the White House than Trump, and he knows it.