I have a serious question and I can't find an answer to -maybe

someone here knows the answer..
Nancy did not start an impeachment inquiry during Trumps first term hoping the election would take care of the problem. It didn't and and Trump (barf ) is (barf ) reelected. Can she start an impeachment inquiry on him in 2021 for things he did in his first term? Oh I am sure he'll collude and obstruct giving her plenty of ammo to use during his second term but for the sake of this post lets say he didn't LOLLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOL. Or does the crime only pertain to the term he is in office and if he is re-elected the slate is wiped clean and we start all over?
Of course this question is assuming we hold the house.

Thanks for anyone who can clear this up for me. I don't remember learning this in civics class but of course who would of thought someone like Trump could ever be elected? This kind of criminal activity in the oval is just scary!!