1) Insisting on complete financial transparency and accountability, including the release of at least the last 5 years of tax forms.
2) Demanding complete divestment form all Trump business enterprises, to avoid possible conflicts of interest.
3) Full and complete cooperation with the effort to investigate any Trump complicity with Russian crimes against the United States such as the hacking of the DNC e-mails, which represent an ongoing threat to our national security.
All three of these things should be done with the threat of impeachment if he does not cooperate. So there are intermediate steps before impeachment, but these have to be insisted upon using the threat of impeachment if there is non-cooperation.