Dianne Feinstein Has to Act

Without Senator Dianne Feinstein, there might never have been an assault weapons ban in 1994. Or the Gun-Free Schools Act of 1994. Or the revelatory report on the C.I.A.’s torture program in 2014. She has had a distinguished career in the U.S. Senate, but her infirmities and illness now force her — and Senate leaders like Charles Schumer — to make a painful choice.

At age 89, Ms. Feinstein is now the Senate’s oldest member, and health issues have kept her out of Washington and the Senate chamber for more than two months,...