General Discussion

There's a process for this.

I'll start with the most common one:

A Member introduces a bill authorizing the Judiciary Committee to open an impeachment inquiry.the resolution is referred to the Judiciary Committee.

If the Judiciary Committee Chairman decides to take up the resolution, the Committee considers it and takes a vote. If a majority of the committee approves the resolution, it is recommended to the floor for action by the full House.

The resolution goes to the floor for consideration. It's debated and voted on. If a majority of House Members approve the resolution, the Judiciary Committee is then authorized to open an impeachment inquiry.

Another way that an inquiry can be opened is upon the action of the Judiciary Committee chairman, who has the authority to initiate an inquiry on his own, either by resolution originating in committee and then sent to the floor or without a resolution but by simply starting the inquiry. However, it is highly unusual for an impeachment inquiry to be initiated by the Judiciary Committee Chairman in Committee - it is more likely for an inquiry in this situation to be initiated by resolution introduced on the floor and referred to Committee for action.

It's interesting that you asked "since when has the constituency decided policy?" I assume this means you're not among those who are citing polls and public opinion as a basis for why an impeachment inquiry should be started now.