John Podesta helped a former Democratic U.S. senator-turned-lobbyist get an invitation to a White House state dinner with the Japanese prime minister in 2015, after leaving the Obama administration.

An email released Thursday by WikiLeaks shows Tom Daschle, a former Senate majority leader from South Dakota, thanked Podesta for his "help" after receiving an invitation to the state dinner with Prime Minister Shinzo Abe at the White House on April 28, 2015. At the time, Daschle had recently set up the Daschle Group, a lobbying subsidiary of law firm Baker Donelson.

Podesta sent an email to Daschle on April 10 with the subject line "Japan," writing, "You set on Abe?"

"If you are referring to the State dinner, yes. I got an invitation yesterday," Daschle wrote back the following day. "Thanks so much, John. I really appreciate the help. We are working with Japan these days on a number of issues."

The exchange took place months after Podesta left his post at the Obama White House to move onto a senior role in Hillary Clinton's nascent presidential campaign.

Obama vowed to keep lobbyists out of his administration and shut the revolving door during his first campaign for president.

At the time of the email exchange, Daschle was serving on an advisory board for the Northeast Maglev, a Washington-based company with a multi-billion-dollar commitment from the Japanese government to build a high-speed train from Washington to New York using "superconducting maglev" rail technology. The company works closely with the Central Japan Railway Company, which has led development of the technology since 1987. Daschle is still on the board.

Daschle referenced the Maglev project in his email to Podesta, seeking "advice" on how to raise the matter with the White House, given that it was a "huge issue" for the Japanese prime minister, who had pledged billions to help build the first leg of the train from D.C. to Maryland. That portion alone will cost an estimated $10 billion.

"I could use your advice on something if you can provide any guidance," Daschle continued. "As you may know, we have been working on an amazing new transportation technology called ‘Maglev.' It already exists in two locations. You may have used it. The first is in China from the Shanghai airport to downtown Shanghai. The second (a newer and even better technology) will be built from Tokyo to Osaka."

"He has raised it three times to both the President and Vice President," Daschle wrote of Abe. "In all three instances, they have not responded to his expressions of interest. He is very frustrated. He wants to raise again on this trip but his staff is afraid that if he does and gets no response for the fourth time, it will trigger the end of Japanese interest."

"They are also hopeful that they could get a memorandum of understanding to share the technology. Once again, we can't get any response from the administration. I have talked to Denis about this. We have tried to engage Foxx and the VP," Daschle continued, referring to White House chief of staff Denis McDonough and Transportation Secretary Anthony Foxx. "We have gotten nowhere."

"I know you are under severe restrictions about any contact with the administration, but if you could offer any advice, I would welcome it," he wrote to Podesta.

Daschle currently serves as founder and CEO of the Daschle Group, which he opened in 2014 after leaving his position as a policy adviser for law firm DLA Piper. Daschle, who represented South Dakota in the U.S. Senate from 1987 to 2004, did not officially register as a lobbyist until March of last year.

The Northeast Maglev has spent more than $2 million lobbying Congress since 2011, according to federal records. DLA Piper is among the lobbying firms that the company has employed. The company is among those identified by USA Today donating to the Bill, Hillary, and Chelsea Clinton Foundation while lobbying the State Department during Hillary Clinton's tenure as secretary of state.

The Northeast Maglev received its first federal funds for the U.S. project—$27.8 million—from the Federal Railroad Administration last November.

The email was published Thursday, in one of the many troves of Podesta's communications released by WikiLeaks in recent weeks. Neither the Clinton campaign nor Daschle returned requests for comment by press time.

The U.S. government has accused Russia of hacking and leaking emails to Wikileaks in an effort to influence the 2016 election.

Daschle endorsed Hillary Clinton for president in May 2016, before she beat out Sen. Bernie Sanders (I., Vt.) in the primary.

"I fully endorse Hillary Clinton's campaign for president because she has the personal strength and conviction to defend the values that South Dakotans and Americans care about most," Daschle said on May 24, pledging to work with Clinton's campaign ahead of the primary in South Dakota.

Leaked emails also show that Podesta was asked by Glen Fukushima, a Japanese-American businessman and former government official, about receiving an invitation to the 2015 state dinner with the Japanese prime minister. Fukushima did attend the dinner as a guest of Sen. Mazie Hirono (D., Hawaii), according to a guest list released by the White House, though it is unclear whether Podesta helped secure his invitation.