The Hollywood Reporter sussed out the evidence. An email from a firm called Extra Mile, soliciting people to be paid $50 to attend "an event in support of Donald Trump and an upcoming exciting announcement he will be making." Instagram photos of an actor in attendance that day. A reference in that email to Gotham Government Relations, the firm that hired Extra Mile and which Trump had used in the past.
Gotham, which put the event together, produced a video of the Trump announcement that it posted on YouTube.
At the time, the revelation didn't make much of a splash. The aftermath of Trump's announcement focused mostly on his comments about immigration. In June 2015, it also didn't seem like it was worth spending a lot of energy on evaluating the then-very-unlikely chance that Trump would go very far in the campaign. This was just a bit of icing on the weird Trump-announcement cake.
What Levine found, though, was that there was another level of detail to those actors showing up. In short: The Trump campaign failed to pay the $12,000 bill from Gotham until about a month after a complaint had been filed with the FEC. The delay between the time Gotham was hired -- June -- and when it was paid -- October -- essentially means that Gotham floated credit to the campaign for those four months, potentially making it a campaign contribution.
Ultimately, the FEC decided that the sum at stake was so small and the lack of information about whether or not such a delay in payment was customary that it wouldn't take action.
That said: Another Trump debt -- the debt that launched his campaign -- was not paid until after someone raised the issue. Just as with Trump's pledge to give $1 million to veterans' groups in January, which also went unpaid for four months.
As of noon Friday, though, all water under the bridge. Whoever showed up to see Trump's announcement, whatever their motivation, that campaign culminates in Trump being the next president of the United States.