When those dates fail, they tend to fail spectacularly. But you rarely have a two-party or multi-party system with one party keeping power for literally decades at a time. One party systems do. They are resilient in their grip on power, not necessarily in the success of the state itself.
Obviously nothing is "permanent" in the sense of being "never ending." If you have permanent custody, you don't control the children forever, just until they turn 18 and you kick them out to fend for themselves, social Darwin style. A "permanent alliance" in Civ still only lasts until the end of the game. But a system that cannot be overturned without severe internal ructions - whether that's a political revolution or a split in the GOP itself - can reasonably be described as "permanent" in this case.
I think we are genuinely at a point where the GOP has entrenched their power for decades, largely due to the stacking of the SCOTUS. Even if the Democrats sweep both Houses, impeach Trump and Pence, and win every seat at every level of government, the SCOTUS will still be stacked until the rapists and fellow conservatives die. The efforts to disenfranchise minority groups are accelerating, and a racist serial rapist sits in the White House. The GOP needs just a little more time to turn this entrenched structural advantage into permanent one party rule.
