Conversation so far:
when did Columbus Delano resign?
1875.
wha did he resign from?
office.
why did he resign?
Bristow threatened to resign if Delano was not replaced.
was he replaced?
Grant replaced Delano with Zachariah Chandler.
what was the corruption?
his personal conduct was exonerated, but his reputation as an honest, capable administrator was damaged, and Delano never again ran for office.
what was he accused of?
extortion.

Question: who accused him?
Self-contained rewrite: who accused Columbus Delano of extortion?