Things escalate quickly in 2018.

On Tuesday night, President Trump held a campaign rally in Tampa. Ahead of that, CNN’s Jim Acosta was accosted by the crowd. Eric Trump, the president’s son, approvingly tweeted a video of the harassment which Trump himself then retweeted.

On CNN Wednesday, Acosta blamed Fox News for stoking the fires of hostility against him and his network. On his Fox News show that evening, Sean Hannity called Acosta “a liberal partisan hack” and said that people were angry at CNN because “[t]hey don’t like your unfair, abusively biased treatment of the president of the United States.” Hannity noted that a study found that Fox News was “among the most trusted brands in TV news.”

Acosta responded on Twitter.

Hannity replied.

On Thursday morning, the president weighed in on behalf of his friend Hannity’s network.

This battle isn’t really about media accuracy — at least, not directly. It, like nearly everything else that touches politics, is about partisanship. And, mirroring the electorate at large, the small part of the country that fervently supports Trump and Fox News has an outsized voice in the conversation.

Hannity is right that Fox News is the news or opinion outlet that’s cited as most trusted in opinion polling. A June Suffolk University poll found that a quarter of Americans identified it as their most trusted source, more than the 14 percent which said CNN or the 8 percent which said MSNBC.

But there’s a reason for that: Fox News is the overwhelming choice of Republicans. More than half of Republicans point to Fox as their most trusted source. CNN is most trusted by Democrats and independents, though only a fifth of each of those groups picks CNN.

Remember that most Americans identify as independent, but generally lean toward one party or the other. Gallup’s most recent partisan identification polling looks like this.

So if half of Republicans trust Fox News more than any other network and 40 percent of Americans are Republican or Republican-leaning independents, that means that the largest unified media-political group is Fox-News-watching Republicans.

Acosta’s correct that Hannity is literally and technically a commentator, not a reporter. His program runs on Fox News as an opinion show and his fervent affection for the president is hardly contained. Hannity often assumes the trappings of objectivity in order to better sell the president, but the intent is obvious.

Hannity’s program was also the most-watched show on cable news in July.

Why? Certainly in large part because Trump is well-liked by Republicans and Hannity’s show reflects that same approach. Critical coverage of the president is not hard to come by, but it’s not what a lot of Trump supporters want to hear.

Which is also why “Fox and Friends” leads in the morning ratings. It attracted about 1.5 million viewers daily in July compared to MSNBC’s 1 million and CNN’s 500,000. Those aren’t huge numbers, but its influence is obvious, given that one of those 1.5 million viewers is the leader of the free world.

The net effect mirrors what we saw in the Republican primary in 2016. A minority of Americans fervently support Trump and therefore tune into Fox News, and that’s enough to power the network to first place in the ratings and to the top of the heap in network trust.

Normally, the tensions between networks and the competition for ratings is friendly, jostling back and forth on a level playing field. Now, though, with Trump’s active encouragement, the media is split into two camps: One loyal to the president and one not. One that Trump advertises from his official Twitter account and one that he disparages as the “enemy of the people.” One which gets jeered at Trump rallies and one which encourages the jeering.

Most Trump supporters seem content with that dichotomy.