The central thesis of the impeachment inquiry into President Trump’s interactions with Ukraine was that Trump was looking for ways to smear former vice president Joe Biden, who led Democratic presidential primary polling throughout 2019. The morning of Trump’s call with Ukrainian President Volodymyr Zelensky, in which Trump pushed Zelensky to investigate Biden, the president was watching a Fox News report that Biden led Trump in national polling. The link between Trump’s interest in Biden and his interest in being reelected seemed obvious, and Trump was impeached.

Earlier this month, though, two things happened in the span of one week that made interest in Biden collapse. The first was that the Senate voted to acquit Trump in his impeachment trial, pushing the Ukraine-Biden story off front pages. The second was that Biden’s front-runner status collapsed after his poor performance in the Iowa caucuses.

The connection between the Iowa results and Biden’s position in the polls is clear. From September through January, he held a steady 30 percent in the polls, give or take. After Iowa he plunged below 20 percent. At the same time, Sen. Bernie Sanders (I-Vt.) and former New York mayor Mike Bloomberg surged.

Trump’s focus changed in that time as well. As House Democrats launched an impeachment inquiry into Trump in September, the president talked about Biden constantly, according to data compiled by Factba.se.

Once Sanders tied for the lead in Iowa and won New Hampshire, Trump talked about Sanders much more. Bloomberg’s hundreds of millions of dollars of advertising, much of it targeting Trump, similarly attracted the president’s attention.

Of course, part of that change is because Trump spends an inordinate amount of time watching cable news, particularly Fox News and the Fox Business Network. On those networks, too, mentions of Bloomberg spiked after New Hampshire. There was likely some causality at play too, with Fox News lifting up Trump’s tweets or Trump tweeting about Fox News.

On Fox News’s competitors, CNN and MSNBC, the same pattern happened. After New Hampshire, Bloomberg was discussed a lot more — in concert with Sanders.

CNN and MSNBC also started talking more about former South Bend, Ind., mayor Pete Buttigieg, with mentions of the winner of the most delegates in Iowa being mentioned 10 times as much the week of Iowa as he had been the week before. (On Fox News, the increase was fivefold.) That talk has faded recently.

On both the Fox networks and their competitors, only Biden was mentioned less frequently in the week after New Hampshire than he had been the week before.

Since last April, Fox News and Fox Business consistently mentioned Biden more than CNN and MSNBC did in any given week. The latter two networks were more likely than the Fox networks to talk about Sanders.

While Trump’s weekly mentions of Bloomberg were closely correlated with both the Fox networks and the CNN-MSNBC total, his pattern of talking about Biden was twice as closely correlated to Fox than to CNN and MSNBC. In other words, it was easier to predict when Trump would talk about Biden based on whether Fox was talking more about Biden than when CNN or MSNBC was talking more about Biden.

Trump and his favorite cable news networks quietly benefited from the overlap of the Iowa caucuses and the end of impeachment. In the past, Fox News has helped amplify politically useful messaging for the president, as when the network embraced Trump’s rhetoric about migrant caravans right before the 2018 election. Once the election passed, so did most of the network’s coverage of the issue, an unsubtle indicator of the motivation for covering it in the first place.

During the impeachment inquiry, Trump and his allies insisted that his actions were properly focused on wrongdoing by Biden. There were efforts to elevate those purported concerns as a demonstration of how serious they were. Once the impeachment fight was over, though, bad-faith elevation of Biden as a bad actor became less urgent and Trump and his allies turned their attention elsewhere.

Had Iowa not happened that same week, we may still have seen Fox News lose interest in talking about Biden and unfounded allegations of his misbehavior in Ukraine. We can’t know, though, how much of the drop in interest was a function of Biden’s fading from importance in the 2020 election.

Clearly, though, Biden’s political stumble has meant that political observers broadly are less interested in discussing what he’s doing. Trump included.