Lt. Gov. Brian Schatz, who is expected to be sworn in today as the late U.S. Sen. Daniel K. Inouye’s successor, said Wednesday that he understands the magnitude of the appointment and promised the islands: "I won’t let you down."

The 40-year-old Hawaii Democrat left for Washington, D.C., Wednesday night with President Barack Obama aboard Air Force One so he could take the oath of office as Hawaii’s senior senator in time to cast potential votes to avert a fiscal cliff of federal tax increases and spending cuts in January.

Gov. Neil Abercrombie selected Schatz on Wednesday over U.S. Rep. Colleen Hanabusa, who was Inouye’s choice as his successor, and Esther Kia‘aina, the deputy director of the state Department of Land and Natural Resources.

The three nominees had been recommended by the Democratic Party of Hawaii’s state central committee, which heard from more than a dozen applicants before deliberating on a short list in a private executive session.

"I’m humbled and honored by this opportunity and obligation to serve the people of Hawaii and the people of America," Schatz said at a news conference with Abercrombie at the state Capitol. "No one can fill Senator Daniel K. Ino­uye’s shoes, but together — all of us — we can try to walk in his footsteps. That means always thinking about what’s best for Hawaii, working together and representing our values and priorities in the nation’s capital.

"And for me, in this position, it means the first step on a very long road."

State Senate President Shan Tsutsui (D, Waihee-Wailuku-Kahului) is next in line of succession as lieutenant governor. He said he would discuss the post with his family and the governor before making a decision. If Tsutsui declines, state House Speaker Calvin Say (D, Palolo-St. Louis Heights-Kaimuki) would be next in line.

Inouye, before he died Dec. 17 at 88 of respiratory complications, had asked Abercrombie in a letter to grant him his "last wish" by naming Hanabusa, 61, who represents urban Honolulu’s 1st Congressional District. The letter was hand-delivered to the governor by Walter Dods, a retired banker, and Jeffrey Watanabe, a retired attorney and chairman of Hawaiian Electric Industries, two of the senator’s closest confidants.

But several sources close to Inouye and Hanabusa had privately predicted over the past several days that Abercrombie would likely choose Schatz. Although the Democratic Party did not publicly release the vote tally, and Abercrombie said the list was given to him alphabetically, sources say Schatz received slightly more votes from the state central committee than Hanabusa and that Kia‘aina was a close third.

Several Democrats said privately that Abercrombie’s decision could cause a schism within the party that could lead to a serious primary challenge to the governor or to Schatz.

Abercrombie is up for re-election in 2014. Schatz will serve until voters in 2014 elect a senator to fill out the remainder of Inouye’s six-year term, which runs through 2016.

"Senator Inouye conveyed his final wish to Governor Abercrombie. While we are very disappointed that it was not honored, it was the governor’s decision to make. We wish Brian Schatz the best of luck," Jennifer Sabas, Inouye’s chief of staff, said in a statement.

Hanabusa congratulated Schatz. "Having served as chair of the Hawaii Senate Judiciary Committee when the succession law was passed, I fully respect the process and the governor’s right to appoint a successor," she said in a statement. "As a member of Hawaii’s congressional delegation, I will continue to work to serve the people of our state, and support our delegation’s efforts."

Schatz will have a slight advantage in seniority over U.S. Rep. Mazie Hirono, who was elected in November to replace the retiring U.S. Sen. Daniel Akaka, and other newly elected senators who are scheduled to take the oath on Jan. 3. Hirono, who will be Hawaii’s junior senator, will be the first Asian-American woman and just the second woman of color to serve in the Senate.

"As a delegation and as a state, we will pull together to build upon the foundation laid by Senators Inouye and Akaka, to ensure that our values and priorities continue to be reflected in our nation’s capitol," Hirono said in a statement.

Abercrombie said that Inouye’s wishes were taken into account.

"The law makes explicitly clear, as does the rules of the Democratic Party, that while everyone’s voice is heard, and everyone’s view is taken into account, nonetheless, no one and nothing is preordained," he said.

The governor said Schatz’s ability to build seniority in the Senate was a factor in his decision, as was the fact that a Hanabusa appointment would have triggered a winner-take-all special election that could have left the 1st District in Republican control. He also said that he took into consideration Hanabusa’s post on the House Armed Services Committee, which is important because of the state’s large military presence.

Asked afterward whether he may have ignited a civil war within the party, Abercrombie said: "If it is an issue for anybody, then I suggest they can take that to the people and present that as an argument. But I think, with regard to 2014, my view is that will take care of itself. My responsibility is to do the right thing by what is in the interest of the party, the state and the country as a whole."

Schatz said he has good relationships with Inouye’s staff and would work toward a smooth transition.

"My job is to reach out to everyone, including and especially key supporters of Senator Inouye — (and) staff members — to make sure that we all stand shoulder-to-shoulder in making sure that this transition is done in a way that’s in the best interest of the state of Hawaii," he said.

Dante Carpenter, the chairman of the Democratic Party of Hawaii, said Schatz would be "under the gun" at first in the Senate because of his lack of experience. He will briefly be the chamber’s youngest senator until U.S. Rep. Christopher Murphy, a 39-year-old Connecticut Democrat, is sworn in in early January.

But Carpenter and other Democrats said Schatz’s potential to establish seniority could be critical to the state over time. No sitting Hawaii senator has ever been defeated at the ballot box since statehood. "In the words of Senator Dan Inouye, invoked more than once: Seniority, in the United States Congress, is everything," Carpenter said.

David Chang, the chairman of the Hawaii Republican Party, which will have to field a candidate from within its depleted ranks to challenge Schatz in two years, said the party wishes Schatz well "even though he lacks the legitimacy of an election and was selected counter to the final dying wish of Senator Inouye."

A.J. Halagao, who worked closely with Schatz during Obama’s 2008 presidential campaign in the islands, called him a natural leader who has proved himself as a member of the state House, a state Democratic Party chairman and as lieutenant governor.

"Brian brings with him a wealth of experience, including legislative experience, foreign relations experience in Asia, D.C. experience as our lieutenant governor, and he’s had to fill in as our governor on a few occasions," Halagao said. "Brian will represent Hawaii well on the national stage."

Jacce Mikulanec, a former policy adviser to Schatz as lieutenant governor, said Schatz is up to the challenge.

"Brian’s 40 years old, he’s run a statewide campaign before, he’s been successful in it, he knows what it takes to win," he said. "I think the governor has made an excellent choice in someone that’s going to be able to not only do the job in Washington, but make sure that he can hold on to the seat come next election."

Schatz said his priorities would be to continue to identify federal money for Hawaii, a Native Hawaiian federal recognition bill, and strategies to respond to global climate change.

He said his wife, Linda, two young children, and his parents would also fly to Washington for the swearing-in.

"To the people of Hawaii, I can assure you this: I will give every fiber of my being to doing a good job for the state of Hawaii," Schatz said. "We have a long and perhaps difficult road ahead of us, but we can succeed if we work together. I understand the magnitude of this obligation and this honor. And I won’t let you down."