[[How can this be constitutional when long ago mail order sales across state lines were ruled exempt under the Commerce Clause?]]
Because now the Supreme court has given the gubmint unfettered control of what it wantrs to tax and force peopel to buy ignoring previous precedence set forth by the courts
Because in that decision the Supremes specifically said Congress was free to authorize interstate sales tax collection if they so desired.
The decision only forbade the states from acting unilaterally without the express permission of Congress.