Earlier quoted context omitted.
> make any Thing but gold and silver Coin a Tender in Payment of Debts Well, they've already violated this by accepting USD, but that doesn't necessarily mean they can just do BTC too. To strike this down the courts would need a lawsuit, though, and I'm not sure who could claim damages. > coin money I take this to mean issuing a currency, which they are not doing here since they don't control BTC.
The federal government is what makes USD legal tender, and this clause does not restrict the federal government. Standing would presumably be with the party which refused bitcoin payment in satisfaction of a debt.
Edit: I'm serious. I'm not saying that's a realistic option.