Donald Trump has appealed a federal judge’s ruling that his $10 billion lawsuit against the IRS was improperly coordinated with his own Justice Department. The ruling matters because it challenges the legitimacy of litigation in which the President sued agencies within his administration and raises wider questions about judicial oversight and the use of public money.

The lawsuit concerned the leaking of Trump’s tax information and sought at least $10 billion in damages from the IRS and Treasury Department. Judge Kathleen Williams found the case was non-adversarial and collusive, after it was linked to a proposed $1.776 billion “anti-weaponisation” fund; Trump is now seeking to overturn that finding on appeal.