Christopher Krebs, a fired Trump official, sues the campaign and the lawyer who said he should be shot.

“Newsmax, the campaign, and diGenova have a symbiotic relationship,” the lawsuit says. “Newsmax disseminates and amplifies the campaign’s and diGenova’s attacks on perceived political threats and allegations of election stealing, which pleases viewers, prompts endorsements from President Trump, increases ratings, supports the political goals of the campaign, and helps raise more money from duped supporters.”

Mr. diGenova, the Trump campaign and Newsmax did not respond immediately to requests for comment.

Mr. Krebs’s lawsuit was filed by the law firm Walden, Macht & Haran in Maryland, Mr. diGenova’s home state, at a moment when Mr. Trump and his allies have brought increasing pressure to bear on Republican officials around the country who have resisted the president’s efforts to tar the elections as compromised by fraud.

The suit notes, for example, that the president has attacked Governors Doug Ducey of Arizona and Brian Kemp of Georgia for failing to assist him in his attempts to overturn the vote counts in their states. It also points out that Mr. Trump and his legal team sought to persuade Republican leaders in states like Pennsylvania to go along with their scheme to “ignore certified election results” and instead have state lawmakers appoint delegates to the Electoral College.

Mr. Krebs, a lifelong Republican, said in a brief interview that he had filed the suit to encourage others from his party not to be “intimidated into silence.”

“We need to make it clear that these behaviors are not acceptable in a civil society,” he said.

Newsmax, which was accused in the suit of aiding and abetting by amplifying Mr. diGenova’s threat, has recently capitalized on Mr. Trump’s displeasure with Fox News and devoted itself to carrying the president’s unsupported claims of massive fraud in the elections. Its prime-time ratings have soared in the process. “People want something that tends to affirm their views and opinions,” Christopher Ruddy, its chief executive, told The New York Times last month.