If Congress cannot, who can? I think treaties must be able to be reneged. And since Congress is signing the treaties, they should also have the power to renege

If Congress cannot, who can? I think treaties must be able to be reneged. And since Congress is signing the treaties, they should also have the power to renege. Now there might be consequences for those actions (the counterparty might attack you, your allies may no longer trust you, etc) and those consequences are what keeps treaties stable. The issue here is that the other party (Native Americans) has no power to enforce the treaty... But IMO, that is a public outrage issue and not a Constitutional issue.