>>> and a voice of moderation and a figure of catastropontroversy has died. today he lost his final battle with cancer and nbc's kelly o'donnell looks back on his life and legacy.
>> reporter: from his days as a scrappy philadelphia prosecutor to decades as that rare washington moderate, arlen specter was often influential and irascible.
>> i have been viewed as who has been accurately characterized as independence, perhaps fierce independence.
>> reporter: admired for how he kept going.
>> i have beaten a lot of tough political opponents.
>> reporter: swept into congress under ronald reagan in 1980 , but specter's views supporting immigration rights, abortion and gun control made him too liberal for the tea party movement. under assault, he bolted to the democratic party .
>> my change in party will enable me to be re-elected.
>> reporter: but specter lost.
>> it's been a great privilege to serve the people of pennsylvania.
>> reporter: he knew controversy well, at the warren commission , he wrote the single bullet theory that explained how lee oswald acting alone assassinated john f. kennedy . he angered many women after the spectacle around anita hill . but specter is also remembered for his wit and his devotion to the senate.
>> i lead with great optimism for the future of our country, a great optimism for the continuing vital rule of the united states senate and the governance of our democracy.
>> arlen specter was 82.