I think the plan is to draw into question where Trump got the money and claim he is using political donations to pay his legal fine.
They want to hit him with campaign finance violations, claiming election funds are being used for private matter.
It wouldn’t be the first time either for such an attempt... the FEC tried to claim Trumps payment to Stormy Daniels was a campaign finance violation. It deadlocked with a 2-2 vote among the FEC panel.
They aren’t that smart.