They filed an affidavit from an insurance broker saying it is "not possible" to find a bond that big. The broker was an expert witness for Trump during the trial.
The trial judge already noted in his decision that this broker was a "close personal friend" of Trump's and had a financial interest in the outcome. A decision could come from the appeals court later this week.
I'm sure the judge will give the broker's opinion all the deference it's due. /s
