Does Tether create systemic risk for the US?

So i understand that Tether has really flourished among global money laundering / US sanction avoidance. All else being equal, I would think the US would move to try and restrict companies/ governments from transacting in Tether, to the extent they can. I read recently that stablecoin issuers are now in the top 20 largest holders of US debt. Is there a point at which they become too large for the US to try and stamp them out without hurting itself at the same time? How big would that have to be? Are we already there?