The political party could not recover from its decline.
It is not easy to turn around a company in decline.
没落 refers to a fall from prosperity or status, often with a sense of ruin. 退勢 focuses on the waning trend rather than the final collapse.
reversing a downward trend; restoring declining fortunes; recovering from a discouraging situation
Standard kanji spelling for 'decline' or 'waning fortunes'.
Rare variant using the non-jōyō kanji 頽; learners should use 退勢.
Compound of 退 (retreat, decline) and 勢 (power, force). The combination conveys the idea of power receding or waning.