I am taking no position here on whether Trump should be impeached or not, but I am curious if the Foreign Corrupt Practices Act can be relevant for the impeachment process (say, because of the dealings with Ukraine and because Trump apparently heads The 2020 Donald Trump presidential campaign).
Impeachment and conviction are entirely a political process carried out by the legislative branch of Government. The question that has to be answered is "has the accused done something sufficiently inappropriate to make it appropriate to remove them from office?"
Something can be legal and still be grounds for impeachment (sex with an intern for example - although in that case the accused was not convicted), or illegal and not be grounds for impeachment (nobody is going to be impeached for a speeding ticket). Having said that, it is quite likely that inappropriate acts will also be illegal but that is not the main question.