It has hardly registered while impeachment consumes the country, but gun control has passed immigration as the issue generating the next most interest online over the last four months, according to data from NewsWhip provided exclusively to Axios.

Why it matters: In a trend that could help shape the 2020 races, immigration — an issue that animates the right — is being usurped by a topic that animates the left.

By the numbers: Through July, stories related to immigration generated 554 million interactions (likes, comments, shares) on social media, while stories related to guns generated 269 million.

But since late August, stories about guns have generated 166 million interactions, compared to 131 million for immigration.

Foreign policy remains the number one topic while Ukraine stays in the news.

Yes, but: The 2020 Democrats have been markedly absent from the gun conversation.

Of the 200 biggest stories about guns in the last four months, the only ones centering on Democratic candidates were about Beto O'Rourke and Kamala Harris — both now out of the race.

Between the lines: Emotion about gun violence often spikes in the aftermath of high-profile shootings, but then disappears after a few weeks.

But after the El Paso and Dayton shootings on the first weekend in August, guns have stayed in the conversation, with a small spike following the shooting at a Naval base in Pensacola, Fla. this month.

Driving the news: The top story related to guns last week was when Houston police chief Art Acevedo railed against Sens. Mitch McConnell, Ted Cruz and John Cornyn for not reauthorizing the Violence Against Women Act or acting on gun violence.

Acevedo: "I don't want to see their little smug faces about how much they care about law enforcement when I'm burying a sergeant because they don't want to piss off the NRA. Make up your minds, whose side are you on?"

CNN's story on the comments generated 513k interactions, more than twice as many as last week's top immigration story (227k).

Our 2020 attention tracker is based on data from NewsWhip exclusively provided to Axios as part of a project that will regularly update throughout the 2020 campaign.

See all past editions of the tracker here.