Statistical analysis suggests 99.9% chance that the Cohen payment to Daniels was a campaign payment
tl;dr - some people noticed that five seemingly "random" campaign payments - ones that didn't appear to be "normal" payments - totaled up to $129,999.72 - with the last payment coming one day before Cohen was told that his bank account had the funds needed to pay off Daniels. They ran 10,000 simulations to get random payments to come near that amount and found that the odds of it getting anywhere near the $130k mark were 1 in 1,000.
My understanding is that the nature of campaign finance's ability to remain someone shrouded in mystery means there will never be a way to fully trace this and create a legal case, but as far as the court of public opinion is concerned...well, I for one am quite willing to believe that the campaign was absolutely financially involved in the payoff.