Here is speculating that Donald Trump has a deep-seeded history with Russians that might have to do with Russians having bailed him out financially when his empire was collapsing. In the process, they learned much about Trump, some of which can be used to blackmail him. What evidence have you?
The suspicious threads lie in the IRS Tax filings and from investigations that stem from them. The evidence is from statements made by his sons. It is in the relationships that his son-in-law has with the Russians and the relationships between Kushner and Trump.
There is another relationship, that of Michael Flynn with the Russians and Saudis and his relationship with Trump.
There is the relationship between Paul Manafort and Trump and a myriad of other persons associated with the campaign.
Therefore, the characterization of speculation moves to anticipation due to the mounting circumstantial evidence that remains below the radar.
As a trained analyst, my prediction is that the smoldering evidence will erupt into a firestorm of indictments. The question is when?