These are among the best songs on this album and a reminder of Ms. Swift’s tenacity. As convincingly as she set out to make herself a country singer a decade ago, she’s applying the same fortitude to much choppier waters and succeeding on her own terms. Though these songs have some of the attitude of pop-punk — a sound she explored a bit on her last album, “Speak Now” — they don’t feel brash. And they show other kinds of growth as well. On “I Knew You Were Trouble,” maybe for the first time, Ms. Swift genuinely paints herself as culpable, an accessory to her own heartbreak. “I knew you were trouble when you walked in,” she sings, “so shame on me now.”

Strikingly, though, each moment of pure pop breakthrough is tempered immediately afterward by a contemplative country moment. “I Knew You Were Trouble” is followed by “All Too Well,” and “22” is chased by “I Almost Do,” the song here that could most convincingly be delivered by a more traditional country singer. After “We Are Never Ever Getting Back Together” comes “Stay Stay Stay,” which features the most gratuitous mandolin on the album.

Ms. Swift has always been a pop star in a country context more than a country star; her trick was in arriving at a time where country could accept such a proposition. She had no direct competition, and the genre’s borders were weakening. But as she ages, country is becoming more and more of a straitjacket, which means going the full Shania Twain isn’t a real option. Ms. Twain had firm country bona fides from the beginning: even as she exploded in popularity, she was still a genre favorite. But Ms. Swift’s country membership has never been that firm.