Sen. Tom Harkin, who has long prioritized the needs of Americans with disabilities, is retiring after 40 years in Congress. (Thinkstock)

After 40 years on Capitol Hill, a U.S. senator who shaped the Americans with Disabilities Act is leaving his post.

Sen. Tom Harkin, D-Iowa, is retiring at the conclusion of the year, after choosing not to seek re-election.

The departure will leave disability advocates without their strongest ally in Congress.

Often inspired by the experiences of his late brother Frank, who was deaf, Harkin has long prioritized the needs of people with disabilities, authoring the landmark ADA and pushing for legislation expanding opportunities for education, independent living, employment and physical accessibility.

“Harkin’s passion to create a world where people with disabilities live independently and are assured of basic equal opportunity has created a lasting and positive impact on the lives of millions of Americans with disabilities,” said Mark Perriello, president and CEO of the American Association of People with Disabilities, who called Harkin the disability community’s “number one champion in Congress.”

“I do not think anyone will replace Harkin, either in spirit or in actuality. I anticipate that many senators will take up various pieces of the disability agenda, but no one will take up the entire cause,” Perriello said.

Sen. Lamar Alexander, R-Tenn., who worked side-by-side with Harkin on the Senate’s Health, Education, Labor and Pensions committee echoed that sentiment.

“Sen. Harkin’s legacy is secure,” Alexander said. “He is the Senate’s champion of Americans with disabilities. It’ll be a long time before there’s a greater champion of Americans with disabilities in this body and I salute him for that.”

Speaking on the Senate floor last week, Harkin urged his colleagues to continue his work.

“We have made significant strides forward in changing America to fulfill two of the four goals of the Americans with Disabilities Act. These two are full participation and equal opportunity,” Harkin said. “The other two goals — independent living and economic self-sufficiency — need more development.”

Specifically, he called on lawmakers to support expanded opportunities for competitive, integrated employment for people with disabilities, acknowledging that he hadn’t done enough in that realm. And, he said more work is needed to further deinstitutionalization of people with disabilities by providing opportunities for “true independent living with supports.”

Harkin also lamented the Senate’s failure to ratify the United Nations Convention on the Rights of Persons with Disabilities.

“I don’t think anything has saddened me more in my 30 years here than the failure of the Senate to ratify the CRPD,” Harkin said. “I hope the next Senate will take this up and join with the rest of the world in helping make changes globally for people with disabilities.”

Noting that he once delivered an entire speech on the Senate floor in sign language, Harkin turned to just one sign to close his time in Congress, pausing to teach those in the chamber the sign for America.

“All of us, interconnected, bound together in a single circle of inclusion with no one left out. This is the ideal America toward which we must always aspire,” he said.