expression, godan verb (-su)
ruin one's reputation in later life; tarnish one's twilight years
Idiomatic expression used when someone who has led a respectable life commits a disgraceful act in old age, damaging their legacy.
あの政治家は晩節を汚してしまった。
That politician ruined his reputation in his later years.
晩節を汚さないように気をつけたい
I want to be careful not to tarnish my twilight years.