The discovery phase happens before trial. The indictment is unsealed and defense gets all the evidence presented to the grand jury. Read the articles of impeachment are unsealed and the defense gets all the evidence presented to the House Intelligence committe, and all other committees conducting the impeachment inquiry.
At the trial in the Senate, Trump may call all the witnesses he wants. I suggest Giuliani. He'd be great!
In the past the discovery phase and the questioning of witnesses took place in public, not behind closed doors. This is bullshit and, unless you are a total Democrat tool, you know it's nothing but a clown show of propaganda. Let Pelosi call a vote.....Get this impeachment underway....But she won't because....And I repeat....There is no evidence. I already asked you guys to publish the now declassified transcript and point to the exact words that you feel support impeachment of a duly elected President. You didn't and you won't and Pelosi is playing games.
Depositions and testimony continue. Evidence is being gathered. Articles of impeachment will be drafted and voted on. The House will discuss the evidence and vote for impeachment. The Articles of impeachment will be made public. Witnesses in the Senate trial will be called. Defense will be proffered.
Nothing being done is unconstitutional, except, of course, the stonewalling by the White House. Subpoenas hold the penalty of law and ignoring such legal means constituents obstruction of justice and contempt of Congress.