This New York Times article suggests that fabricating evidence is what Giuliani is angling to do:
VIENNA — They were two Ukrainian oligarchs with American legal problems. One had been indicted on federal bribery charges. The other was embroiled in a vast banking scandal and was reported to be under investigation by the F.B.I.
And they had one more thing in common: Both had been singled out by Rudolph W. Giuliani and pressed to assist in his wide-ranging hunt for information damaging to one of President Trump’s leading political rivals, former Vice President Joseph R. Biden Jr.
That effort culminated in the July 25 phone call between the American and Ukrainian presidents that has taken Mr. Trump to the brink of impeachment and inexorably brought Mr. Giuliani’s Ukrainian shadow campaign into the light.
But interviews with the two Ukrainian oligarchs — Dmitry Firtash and Ihor Kolomoisky — as well as with several other people with knowledge of Mr. Giuliani’s dealings, point to a new dimension in his exertions on behalf of his client, Mr. Trump. Taken together, they depict a strategy clearly aimed at leveraging information from politically powerful but legally vulnerable foreign citizens.
How to assess new information: Don't ignore the old information
When the new information surfaces, one can ask by what measure should the new information by assessed? That is an excellent question. It's the key question.The answer is to apply reasonable, logical measures of transparency and credibility to the new information in view of existing information. If the Senate investigation finds legitimate evidence of significant bad acts by Biden and/or Ukraine in the 2016 election, and is transparent about the sources and their credibility, then that evidence has to be accepted as real and given whatever reasonable probative weight it deserves.
However, one can reasonably expect that any new evidence that comes out from the Senate investigation will have to contradict existing contrary evidence. That's the point of building new conspiracy theories. If the origins or sources of the new evidence are not credible, and/or opaque or not revealed, e.g., for 'national security' reasons, then one can reasonably conclude that the GOP has now fallen so far into immorality that it is now willing to fabricate or rely on fabricated false evidence to lie to and deceive the American people for purely partisan gain.
If one wants to be fair and rational about this, these facts (not opinions) need to be kept in mind. Solid evidence already exists that shows (1) the Ukraine was not involved in the 2016 attacks on the US election, (2) Russia orchestrated the 2016 attacks on the US election, and (3) Trump[1] and his enablers, e.g., Rudy Giuliani,[2] are chronic liars who do not hesitate to lie, withhold information and emotionally manipulate to distract, deceive and confuse the American people. Those people would not hesitate to fabricate evidence to support the new conspiracy theory.
Whatever evidence the Senate comes up with has to (a) properly take existing evidence into account and render it not persuasive, and (b) be transparent in view of the mountain of lies and deceit the GOP has operated with since Trump came to power. In other words, existing evidence of lies, deceit and manipulation by Trump and the GOP means that they get no benefit of any doubt because they earned and fully deserve deep public distrust.
Footnotes:
1. The president's track record of false and misleading statements to the public is staggering. That constitutes solid evidence of his deeply immoral character. The existing herd of admitted or convicted felons the president has surrounded himself is more evidence of the president's immoral character.
2. In response to being asked what he would do if the president decided to 'throw him under the bus', Mr Giuliani responded with this retort: "I have insurance". That means that Mr. Giuliani probably has information that incriminated the president in illegal acts. What other kind of insurance would the president fear? It is hard to embarrass a man who isn't fazed by his acts and lies, e.g., sex with porn stars or the tape where he brags about sexually assaulting women. This is more evidence of the sleaze and immorality that the president and his enablers operate by. Given his behavior after prior gaffes, it is reasonable to expect Giuliani will deflect or distort his insurance comment by saying he did not mean that he had any evidence against the president.