International relations, defense, and tariffs? Issues covered by the Constitution. Mysteriously enough, primaries are not. The Article reads specifically
"The times, places and manner of holding elections for Senators and Representatives"
I agree Congress should be in charge of the election, however there is no mention of how the candidates are chosen. Therefore, a state issue
The NJ Supreme Court decision affected the ballot that would appear on election day, making it subject to Federal regulation.
Further, the decision was that of the NJ Court and not the State Legislature, which is also in violation of Article 1, Section 4.
When the Jersey Supreme Idiots based their vacation of Jersey election law not on the law, nor on any authority granted it by the US Constitution, Congress or the NJ legislature to rule on election law with regard to Senate elections, that vacation became unconstitutional (regardless of SCOTUS' lack of review).