If you mean a national org I guess PSL would be it. FRSO is mostly irrelevant and varies a lot chapter to chapter, some of which are even endorsing local lib politicians which at least PSL never does. WWP is also irrelevant and mostly boomers, albeit nice ones. DSA is a colonial project masquerading as leftist to trick newly radicalized people.

As far as upholding treaties goes, this is one of the most common and largest rallying cries of Indigenous people in the US today, so that position is probably taken up by orgs like FRSO because they do not have Indigenous people internally to rely on for this and it is what a lot of Indigenous people openly advocate for. It isn't revolutionary compared to the abolition of the US government entirely and return of all land to the formerly colonized subjects but it is revolutionary if you think about how the new democracy movement in china was revolutionary for the time.