If the talks are going nowhere, Trump should leave.
He would simply be doing what Reagan did in the Reykjavik Summit with Gorbachev in 1986.
Reagan refused Gorbachev’s demand NOT to implement the Strategic Defense Initiative (SDI). When it was clear that this was the sore point of the discussion and Gorbachev would not budge, he walked away.
...later getting what he wanted without compromising a non-negotiable.
I think Trump is of the same ilk as Reagan.