U.S. Sen. Daniel Inouye speaks at the Japanese Cultural Center on Nov. 6 in Honolulu. (Marco Garcia/Associated Press)

The death of Sen. Daniel K. Inouye (D-Hawaii) brings immediate changes to the power structure of the U.S. Senate.

First, Inouye’s death from respiratory complications prompted a change in the line of presidential succession. As the most-senior member of the majority party, Inouye served as Senate President Pro Tempore, making him third in line to the presidency behind Vice President Biden and House Speaker John A. Boehner (R-Ohio).

Less than two hours after Inouye’s died, the Senate passed a resolution naming Sen. Patrick Leahy (D-Vt.) as the new president pro tempore. Leahy was first elected to the Senate in 1974.

By tradition, the “President pro tem” is expected to preside over the Senate in the absence of the vice president. But tradition also dictates that presiding duties fall to the most-junior members of the majority party so that they may learn the arcane procedural rules of the chamber.

Inouye was the second-longest serving senator in U.S. history, behind Sen. Robert C. Byrd (D-W. Va.), who died in 2010. He was first elected to the House in 1959 — the year Hawaii became a state — and won his Senate seat in 1962.

“Tomorrow will be the first day since Hawaii became a state in 1959 that Dan Inouye will not be representing us in Congress,” Sen. Daniel A. Akaka (D-Hawaii) said in an emotional tribute to his colleague Monday night. “Every child born in Hawaii will learn of Dan Inouye, a man who changed the islands forever.”

Inouye’s death — and Akaka’s impending retirement — also marks a significant generational shift in Senate history: Sen. Frank Lautenberg (D-N.J.) will be the only — and likely the final — veteran of World War II serving in the Senate next year.

The death of Hawaii’s senior senator also creates a vacancy atop the powerful Senate Appropriations Committee. Here too Leahy is next in line, giving him the right of first refusal to the chairman’s gavel. Leahy currently serves as chairman of the Senate Judiciary Committee, and if he passes on the appropriations post — an unlikely scenario considering the clout that comes with being appropriations chair — Sen. Barbara A. Mikulski (D-Md.) would be next in line on the committee.

Tributes to Inouye began pouring in shortly after Senate Majority Leader Harry M. Reid (D-Nev.) noted his passing in a dramatic announcement on the Senate floor.

Sen. John McCain (R-Ariz.) regularly clashed with Inouye over appropriations matters and noted their disagreements Monday evening. But McCain added that “No one — no one — ever, ever accused Dan Inouye of partisanship or unfairness. He loved Native Americans and he loved his Hawaiians.”

Leahy called Inouye “A man of few words, most importantly he was a man of his word. I have always admired his diligence, his character and his willing bipartisanship as a legislator.”

From across the aisle, Sen. Rob Portman (R-Ohio) called Inouye “a true role model, not only for his acts of valor as a hero in World War II and his extraordinary service to our country as one of the nation’s longest-serving Senators, but also for his humility and graciousness.”

“He was a counselor to younger members like me, a great listener, and a Senator who always put his nation and the people of Hawaii ahead of partisan politics and his own ambition,” Portman said.

For his part, Akaka fought back tears as he recalled his years of service alongside Inouye.

“His legacy is not only the loving family that he leaves behind, it can be seen in every mile of every road in Hawaii, in every nature preserve and every facility that makes Hawaii a safer place. He fulfilled his dream of creating a better Hawaii,” Akaka said.

Paul Kane contributed to this report.

This item has been updated.

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