Sinclair Broadcast Group’s headquarters in Hunt Valley, Md., seen in 2004. (Steve Ruark/Associated Press)

Two months before Monday’s announcement that Sinclair Broadcast Group would pay $3.9 billion for Tribune Media and add to its dominance as the nation’s largest owner of local TV stations, a top executive at Sinclair beamed a short commentary piece to many of the company’s 173 stations.

In the segment, which looks like it belongs in a newscast, Sinclair vice president for news Scott Livingston stands before a wall of video monitors and warns that “some members of the national media are using their platforms to push their own personal bias and agenda to control exactly what people think.” He accuses the national media of publishing “fake news stories” — a direct echo of President Trump’s frequent complaint — and then asks viewers to visit the station’s website to share “content concerns.”

The piece was a “must-run,” meaning news directors and station managers from Baltimore to Seattle had to find room for it. While other station owners also push “must-runs,” typically station promotions, Sinclair appears unique among broadcasters for what some analysts see as a political slant to its programming — from news coverage and must-runs sent by headquarters critical of Democrats to last month’s hiring of Boris Epshteyn, a former Trump White House official, as Sinclair’s chief political analyst.

In Seattle, where Sinclair owns KOMO-TV, some newsroom staffers complained to their union that the must-run spot interfered with their jobs as journalists.

“The must-runs look like they are part of the news,” David Twedell, business manager of a local camera workers’ union in Seattle, said. “And they’re clearly not.”

Now, Sinclair’s approach could be tested as it expands to where Tribune operates: some of the most valuable and largest markets in the country, including New York, Los Angeles and Chicago. Sinclair historically has dominated small and mid-size markets, such as Nashville and Oklahoma City.

Buying Tribune would grow Sinclair from 173 TV stations to 215 stations nationwide, giving it unprecedented exposure to the nation’s TV viewers and raising the possibility that federal regulators will force Sinclair to sell some stations to avoid violating long-standing rules intended to prevent a single company from running too many stations.

Sinclair, family controlled and based in Hunt Valley, Md., north of Baltimore, beat out 21st Century Fox to acquire Tribune, the Chicago-based broadcasting company that also owns stakes in the Food Network and CareerBuilder. The deal calls for Sinclair to acquire 100 percent of the company for $43.50 a share, plus the assumption of about $2.7 billion in Tribune debt, according to the companies.

The deal also has energized long-running speculation that the quiet company has ambitions to be the broadcast world’s Fox News. For some journalists at KOMO in Seattle, that is not something they want to be associated with, Twedell said. That “must-run” on fake news was just the latest in a series of such requests.

“That’s what bothers us the most,” he said.

While partisan coverage is a familiar staple of cable networks — Fox News on the right, MSNBC on the left — it remains mostly unheard of in broadcast TV, where it has generally been accepted that public airwaves should be used in the difficult-to-define public interest.

Local TV stations rank high in public trust, and that is partly because they avoid delving into divisive topics such as national politics, said Harry A. Jessell, editor of TVNewsCheck, a TV broadcasters trade publication.

Sinclair executives such as Livingtston see it differently, Jessell said. They believe they are pushing back against what they see as a liberal bias in most news programming.

Livingston “sees himself like an old-fashioned newspaper publisher, one with a point of view,” Jessell said.

In recent years, Sinclair-run stations have earned a reputation for conservative-leaning content. Industry experts say that contrasts with local Fox affiliates, which share part of a name and a corporate owner with Fox News but have not strayed toward one side of the political spectrum.

“You don’t see the same kind of top-down news philosophy that we see at Sinclair,” said Matt Wood, policy director at Fair Press, a nonpartisan advocacy group that opposes media consolidation.

In 2004, when John F. Kerry was running for president, a public backlash that hit Sinclair’s stock price forced the company to back off plans to have its stations air a documentary called “Stolen Honor: Wounds that Never Heal,” which carried a strident anti-Kerry tone. Instead, Sinclair stations aired an excerpt.

In 2012, Sinclair stations in several battleground states aired a half-hour news segment that faulted President Barack Obama for his handling of the economy and the terrorist attack in Benghazi, Libya. Democrats criticized that decision.

Last fall, Sinclair was accused by Democrats of providing Trump, then a candidate, with in-depth interviews and friendly coverage that it did not give Trump’s challenger, Hillary Clinton.

Sinclair responded that it offered Clinton’s campaign the same opportunities and did not hear back.

Jared Kushner, Trump’s son-in-law and now a White House adviser, told supporters that Sinclair and Trump’s campaign had struck a deal for favorable coverage, a claim denied by other Trump officials, according to Politico.

Sinclair’s current roster of 173 stations are concentrated in smaller markets such as Green Bay, Wis., Scranton, Penn., and Cincinnati. While absent from some of the nation’s biggest cities, Sinclair’s broadcasts reach people who are influential when it comes to presidential politics.

“It’s almost as if they were built for this, what happens every four years, with this natural expansion of theirs into battleground states such as Wisconsin, Michigan, Ohio,” Wood said.

Sinclair did not respond to a request for comment.

Some of the changes that come with Sinclair ownership became apparent in Washington in 2014, when WJLA-TV was bought by Sinclair, part of an eight-station deal with Allbritton Communications for $985 million.

The new owners added commentaries from Mark Hyman, a Sinclair executive and conservative pundit. It started regular public-affairs programs produced from Washington and hosted by conservatives Sharyl Attkisson and Armstrong Williams, who served as Ben Carson’s business manager during Carson’s presidential campaign.

Aside from concerns about Sinclair’s leanings, critics of the Sinclair-Tribune deal also worry about the effects from the increasing consolidation of broadcast station owners.

Federal Communications Commission rules limit any single station owner to reaching 39 percent of the national TV audience and prohibits ownership of more than two stations in most TV markets.

But the FCC offers exceptions and waivers to those rules — including a 50 percent discount in the viewership reach of UHF channels.

The UHF rule dates back to 1985, when the broadcast dial was split between VHF (Channel 13 and below) and the weaker-signal UHF (Channel 14 and higher). That difference was mostly eliminated with the switch to digital broadcast TV.

FCC Chairman Ajit Pai, a Republican elevated to his post by Trump earlier this year, has stated repeatedly that he favors loosening the ownership standards, especially in light of increased competition.

A Sinclair-Tribune combination would boost the company from just under 39 percent of the nation’s TV audience to nearly 45 percent, according to Free Press. Remove the UHF discount, and an expanded Sinclair would have stations reaching 70 percent of the nation.

Mark Fratrik, chief economist at advisory firm BIA/Kelsey, said the FCC’s move toward relaxing strict ownership rules reflects a media landscape where broadcast TV no longer dominates. He pointed to the FCC’s ban on owning both a daily newspaper and TV station in the same city, which has been in place since the 1970s. That makes less sense today.

“Deregulation benefits the entire TV industry and makes it more competitive with all these new options,” Fratrik said.

Paul Farhi contributed to this story.