Senator Dianne Feinstein, the trailblazing Democratic power broker who served in the Senate for 30 years, died on Thursday night, according to a family member.

In recent years, Ms. Feinstein, 90, had suffered from frail health and memory issues that made it difficult for her to function alone and prompted calls for her to step down, which she consistently rejected.

Her staff was being informed at 9 a.m.

A spokesman for Ms. Feinstein’s office did not immediately respond to a request for comment.

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