If Texas had tried to enforce the deadline in 2008, they would have lost in court. The right of a major political party to have its presidential candidate on the ballot is contingent on it holding a presidential preference primary and base a substantial share of its delegates to the national convention allocated on the basis of the results.

If the deadline were enforced, a Texas political party would not be able to associate with a national political party of its choice, even though Texas law requires such association.

The only legitimate State interest in a deadline would be to have enough time to have ballots printed, but the SoS had no problem certifying the candidates to the county election authorities by the certification deadline in State law.

Political parties must qualify to have their presidential candidate on the ballot at roughly the same time as an independent presidential candidate does. So there really isn’t a difference, except that in one case the ultimate choice of the candidate is vested in the party; and in the other case, it is vested in the candidate himself.