Yglesias zooms out:

[N]obody lasts in office forever, no congressional majority lasts forever, and no party controls the White House forever. But the measure of a political coalition isn’t how long it lasted, but what it achieved. From the tone of a lot of present-day political commentary you’d think that the big mistake Lyndon Johnson made during his tenure in the White House was that by passing the Civil Rights Act he wound up damaging the Democratic Party politically by opening the South up to the GOP.

Back on planet normal, that’s the crowning achievement of his presidency.