Sinclair Broadcast Group's proposed $3.9 billion acquisition of Tribune Media would give the conservative-leaning company control of an additional TV station in Des Moines, Iowa — one of the most important presidential primary media markets in the country.

Why it matters: Sinclair's possible acquisition of an NBC affiliate in Des Moines (WHO-DT) underscores Democrats' worries about the deal giving a right-leaning company significantly more control over local news. The Sinclair-Tribune deal is expected to be approved by regulators this quarter.

Sinclair already owns KDSM in Des Moines, which received roughly $295,000 of political ad dollars during the 2016 primaries.

The Tribune-owned NBC channel (WHO-DT), meanwhile, captured roughly $1.6 million of political primary ad spend in the last cycle, according to FCC filings.

Sinclair also already has a significant footprint in other major primary states. It owns a station in Portland, Maine that covers parts of New Hampshire, and stations in four different South Carolina markets, as well as Savannah, which reaches southern parts of state.

FCC Commissioner Jessica Rosenworcel, a Democrat, tells us in a statement: "Americans rely on local news to understand everything from communities to campaigns and when one company alone can reach 72% of our households, they have extraordinary power to influence what we see, hear, and learn. The unprecedented size of this proposed merger should have us all concerned."

How it works: Until recently, it would have been against FCC rules for Sinclair to own both WHO-DT and KDSM because each is one of the top four stations in Des Moines. Under a change approved along party lines in November that's expected to take effect next month, however, the FCC can waive that prohibition on a case-by-case basis. That means that this aspect of the Sinclair-Tribune deal could become an early test of FCC Chairman Ajit Pai's massive media deregulation agenda.

Don’t forget: We still don't know which stations the Department of Justice might push Sinclair to divest to get the deal through.

Why local news matters: Local news is still the most popular way for people in America to get their news — something merger opponents fear could be exploited if a conservative-leaning broadcaster reaches 70%+ of American households. Furthermore, local news is the only medium that is more heavily consumed by less educated, less wealthy Americans, according to Pew.

This post has been updated to correct Sinclair Broadcast Group's full corporate name.