President Donald Trump escalated his attacks on the media on Sunday, calling on the Federal Communications Commission to investigate the polling used by news outlets and to punish a prominent television news host.

Trump has long maintained an adversarial relationship with journalists and news organizations that publish stories he dislikes, particularly coverage of his standing in the polls. Numerous recent polls show Trump with the lowest approval rating of either of his terms in office, as the unpopular Iran war continues and gas prices remain high. He has increasingly channeled his animosity toward the press into demands for action by the FCC, which controls broadcast licensing. The First Amendment to the US Constitution explicitly protects freedom of the press and freedom of speech, and legal experts have long held that the government cannot revoke or condition broadcast licenses based on a station's news coverage, a principle reinforced in the Supreme Court's Red Lion and Fox Television decisions barring licensing power from being used to censor editorial content.

In a social media post, Trump complained Sunday that something must be done about "fake polls" used by the news media, declaring: "FCC TO THE RESCUE!" Polls are often sponsored by television networks or news organizations, but are conducted by universities or polling companies over which the FCC has no control. The agency also has no authority over cable stations or print media.

In the same series of Sunday morning posts, the president lashed out at Kristen Welker, the moderator of NBC's Meet the Press, for saying that his endorsements of Republican candidates in this year's primary elections had shown mixed results. Earlier in the week, he attacked New York Times reporter Maggie Haberman for reporting that he was skipping the annual Sept. 11 commemoration in New York this year because he would not have a speaking role.

"How can anyone be allowed to say this, working for freely given Public Airwaves?" Trump said of Welker's reporting. "Because of this purposeful inaccuracy, she will be reported to the FCC for rebuke or punishment."

Short of canceling NBC's broadcast license, there is little the Trump administration can legally do to punish Welker for her reporting. Threatening to do so would put the White House in tension with a decades-old norm under which administrations have generally avoided direct pressure on the FCC, an independent agency whose five commissioners are appointed to fixed terms, precisely to insulate licensing decisions from political interference.

"Kristen is one of the best in the business and we stand by her," an NBC spokesperson said in an emailed statement.

A handful of the candidates Trump endorsed this year did not win their primaries or special elections. However, some of his prominent endorsements did win, including the special election that elevated Darline Graham to replace her late brother, Lindsey Graham, in the Senate.

Trump urged the FCC's chairman to follow up on his complaints, writing: "I hope that Chairman Brendan Carr, and the fine people of his Commission, will take this Threat to our Country very seriously." Carr, whom Trump first appointed to the commission during his first term, has previously pursued investigations into broadcast outlets, and how the agency responds to these demands is likely to be watched closely as a test of its independence.

This story was originally featured on Fortune.com.