Trump was absolutely correct that Zelensky doesn't have any cards, but as of the fall of Kursk, neither has Trump. It's not his fault, but it is what it is.

• Weapons? Useless.
• Sanctions? Not very effective.
• Direct military reinforcement? Out of the question.
• Kursk? Fallen.

The only thing Putin has to lose is more of his men in the course of the war, but I'd guess the majority of Russian soldiers and civilians believe the fight is worth it at this point. Russia will whoop on Ukraine some more and eventually there won't be anything to negotiate with.