That they did nothing is an assumption that you have made. Sinema and Manchin are beholden to nobody except their constituents, so there isn't much that anybody in the Senate can do to them. Should we become like Republicans and censure those who don't vote the way that we want? If so, can you possibly see any chance that this would backfire? Various Senators did tried negotiating with them! That's something, right? Why is your first assumption that there was anything that other Dems could have done that would have changed the outcome? Sanders didn't get either one to change their mind, so I guess he's useless too!