Joseph Lieberman, the former Connecticut senator and Democratic vice presidential candidate, is working for a company he once called a national security threat.

In November, Lieberman registered as a lobbyist for ZTE, a Chinese telecom giant with close links to the country’s government.

The ex-senator told Politico that, despite his registration, he wouldn’t actually be lobbying for the firm. Rather, he hoped to “raise the level of trust in ZTE.” Lieberman certainly should understand the trust deficit the company faces. In 2010, he signed a letter saying ZTE and another Chinese telecom company, Huawei, could threaten American national security.

“We are very concerned that these companies are being financed by the Chinese government and are potentially subject to significant influence by the Chinese military which may create an opportunity for manipulation of switches, routers, or software embedded in American telecommunications network so that communications can be disrupted, intercepted, tampered with, or purposely misrouted,” the letter said. “This would pose a real threat to our national security.”

The letter, sent to the chairman of the Federal Communications Commission, also raised concerns about ZTE’s close links to the Chinese military.

“Has the FCC monitored the sale of foreign telecommunications equipment, software or services to U.S. carriers?” the letter said. “How much of this equipment has been manufactured, produced or provided by companies like Huawei and ZTE that are closely linked to a foreign government and/or foreign military?”

In the years since then, Lieberman has taken a different tone. He told Politico he may help ZTE “try to reassure both their consumers in America and also obviously the U.S. government.”

Reached for comment, Lieberman told The Daily Beast that his past criticism of ZTE was actually an asset as he sought to improve the company’s image domestically.

“ZTE asked me to lead this independent inquiry precisely because of—not in spite of—the fact that I share many of the concerns of the Senators and others in the U.S.G. whose views ZTE wants to understand and address,” he said in a statement. “Because I have demonstrated that I share their concerns, ZTE believes my inquiry can engender candid and constructive dialogue that could lead to effective solutions.”

Lieberman has his work cut out for him. In 2017, ZTE admitted to violating U.S. sanctions on Iran by illegally shipping goods to the country. And the company’s close relationship with the Chinese government has concerned lawmakers on both sides of the aisle. Dan Blumenthal, the director of Asian Studies at the American Enterprise Institute, said there’s emerging consensus that the company threatens the U.S.

“Companies like ZTE and Huawei and some others want to dominate the next generation of 5G and mobile technology, and that poses a national security risk to the U.S. and our allies as well as a risk to the future of U.S. economic leadership,” he said.

“For all intents and purposes, they’re an organ of the Chinese Communist Party,” he added.

Lieberman’s work for ZTE has already drawn criticism. The Campaign Legal Center, a government watchdog group, called for him to register as a foreign agent because of the company’s close links to the Chinese government. And Brendan Fischer, who heads the group’s Federal Reform Program, called Lieberman’s work for ZTE “swampy.”

“It is unseemly, but not uncommon, for a senator who supported, say, the oil and gas industry to then lobby for that industry after leaving office,” he told The Daily Beast. “But it is something else altogether when a former member takes one side of an issue while in office, and after leaving office pushes the opposite side of that issue in exchange for a check.”“It is bad enough that Lieberman is working on behalf of a foreign corporation that violated U.S. sanctions and poses national security concerns,” he added. “It is even worse that he recognized those concerns as a senator, and is working on ZTE’s behalf anyway.”