From +9 to +3.8 since the hearings started

Idea that the impeachment hearings would solidify support was wrong!

Keep in mind that Democrats went to public hearings in part to shore up support. Everyone instinctively knows that you cannot remove a duly elected President based entirely on partisan support (even Pelosi knows that). The ONLY way this was successful for Democrats was for these hearings to push the needle in their favor and start to pick up right leaning independents, as well as some Republicans.

But In spite of controlling all aspects of these hearings and in spite of calling only those witnesses and asking only the questions that they want to ask and in spite of withholding exculpatory evidence and in spite of not allowing the President to cross examine or call witnesses... they have still managed to lose (not gain) support.

This comes from two fundamental issues. The first is that the allegations are primarily smoke and mirrors. There isn't really a concrete issue that the general public can look at. The Democrats can demand that certain actions constitute "bribery" but there really isn't a good foundation for this belief (never before has setting conditions for aid argued to be bribery). People want to be able to easily understand a crime, especially when it comes to removing a President from office for the first time "ever". 

The second issue is that the Democrats have simply not been able to push forward their case. Witness after witness after witness has provided the same basic testimony. They complain about the President's foreign policy. They provide some hearsay information. They demand that what they believe happened was "inappropriate". But once each witness is questioned directly as to whether or not they witnessed any crime... they all say that they have not.

Hard to impeach a President when nobody you call to the stand will testify that they have witnessed any crimes.