This is really unbelievable BS I am afraid, In the present process there was no real evidence of wrongdoing by Trump and the farce was exposed for what it really was - an effort to get Trump out of the 2020 election.
The DP wants to use the following for that purpose:-
* Some comments from the Mueller report on Russian interference in the 2016 election and a statement made by Mueller during a House Hearing that the Russians acted to help Trump in that election; and
* The Bolton saga.
The former won't work - neither will the latter. Let me be more explicit - Trump effectively fired Bolton as National Security Advisor, The latter wrote a book about his involvement in the Trump Administration. Since it is the norm and judicially required that such a book needs a review by the NSC to ensure that state secrets are not exposed in the book, the manuscript was sent to the NSC and two days after Bolton's agent receives a letter saying there was indeed state secrets in the book and they asked he agent and Bolton to participate in an exercise to have those reviewed, the manuscript was leaked to the New York Times.
It is not clear how the leak occurred - but it is obvious that the whole idea was to use the manuscript in a desperate effort to get support for he Trump Impeachment from that manuscript. Can the Manuscript be used for anything in a legal context without clearance from the NSC? The answer is a definite NO. The manuscript review is first to be completed by the NSC and if after that there is any reference to Ukraine left what is left can be used.
What has already been in the NYT and in speeches by the House Managers in the present Impeachment Trial could also be illegal and could lead to judicial proceedings against the people involved. That is unlikely to be legally usable in any new Impeachment charges. Not that that would bother the House Democrats - they did everything possible to avoid legal precedents in the present case,
I think the DP has a problem - they have crap candidates to oppose Trump in 2020 and they know that -
* court cases are on the cards as to the 2016 selection and that could be a serious if not fatal impact on the Obama Administration and the DP; and
* a further investigation off fraud in Ukraine will expose the involvement of not only the Biden's, but a whole list of DP senor members in Ukraine and Russian corruption.
The only way those investigations and court cases could be avoided is by getting rid of Trump and hope his successor would not go further with investigations and criminal charges against the DP leadership cadre.
The short answer is even though there are some establishment Senators who dislike Trump and is in sympathy with some DP members and even supported DP candidates in 2016 - they are not going to be able to convince others that they should play the DP game.