I am asking you what leverage you think they have over the US specifically to extract such a massive and politically charged concession.
The financial and military resources intended to keep Ukraine viable are drawn down to about 1/9th of what was allocated in total. There's no way to keep funding the fighting without depleting equipment intended for other priorities (Israel, Taiwan, etc.).
The very current news of the US telling Ukraine to figure out a peace concession that would gain Russian agreement certainly sounds like this shindig is up. So rather than saying this is about Russian leverage over the US, mainstream Western media is even signalling very clearly that US leadership wants this to end.
In that sense, you could say Russia's greatest leverage is simply to keep this war alive and perhaps even signal at ramping up.