Then why did it allow the Supreme Court to rule on Texas v White?
Beats me. Its reads like a pretty nonsensical decision.
“Texas had never been outside the Union” is a pretty absurd statement, given that state that Texas was in at the time (occupied and without representation in Congress).
On the other hand, I could just be wrong:
Chase did oppose Daviss trial, both privately and in his official capacity as Chief Justice, but not because he endorsed Daviss take on the legality of secession.[15] Privately, he agreed with those in the north who favored leniency for former rebels.[16] Publicly, as one of the presiding judges in Daviss trial, Chase also favored ending the proceedings. His reason for doing so, however, turned not upon the question of secession, but rather on his interpretation of the Fourteenth Amendments third section.[17] This provision, which barred former Confederates like Davis from holding public office (absent approval by two-thirds of Congress), was viewed by Chase as imposing a punishment for treason. That being the case, a treason trial of Davis would violate the Fifth Amendments prohibition upon Double Jeopardy, since it would seek to punish him again for the same offense.[18] (Similarly, when seeking to have the treason indictment dismissed, Daviss lawyers didnt raise the constitutionality of secession as a defense.[19] Rather, they focused on the Fourteenth Amendment,[20] along with general considerations of justice.[21])