A lawyers principle duty is to themselves. So every case is winnable if the client is rich enough to pay.
If this case is a slam dunk you'd have lawyers queuing lining around the block to do it on a no win no fee basis. Even the firms that Trump has strong armed into providing him with pro bono work will be running a mile.
Anyway it's not the legal side that's an issue. What happens if Trump announces he will tariff the UK at 1000% unless he gets $1 billion from the "BBC" ? With the traitors in Reform and GBNews cheering him on ?