[heroprotagonist]

Do these kind of things ever actually expire though?

All the 'temporary' powers granted with an expiration period have been renewed or expanded for the last 30 years. Often as little-noted riders on lesser bills of questionable relation, or bundled as side notes into major debacles like threats of government shutdown.

[newZWhoDis]

Federal income tax was supposed to be temporary for WWII, we see how that worked out.

[rsync]

Federal income tax, while extant in some ways prior, was broadly established in 1913 with the 16th amendment[1].

Other than very high war profiteering tax rates imposed during WWII - which were not only refundable but also removed over time - there is almost no connection at all between WWII and the broad concept of federal income tax.

[1] https://en.wikipedia.org/wiki/Sixteenth_Amendment_to_the_Uni...