Senate stalwart Diane Feinstein died Thursday at the age of 90. Today, we talk about her legacy — and the existential crisis for Democrats that comes with her vacant Senate seat. Read more:Sen. Dianne Feinstein, centrist stalwart of the U.S. Senate, died Thursday. At age 90, she was the chamber’s oldest sitting member and its longest-serving woman.Although the question of her fitness to serve received increasing scrutiny after she was hospitalized in February, Feinstein worked in politics for more than 50 years. She started in local politics in her home city of San Francisco and  eventually became the city’s mayor. Then, in 1992, Feinstein became the first woman elected to the Senate from the state of California.Today, senior congressional correspondent Paul Kane discusses the late senator’s life, legacy and the big question on the minds of many on Capitol Hill: What will happen to her vacant Senate seat?