A one-second video clip was at the heart of a Tuesday spat between President Trump and one of his favorite foils, CNN.

The Trump campaign lashed out after it said CNN refused to run an advertisement highlighting Trump’s accomplishments during his first 100 days in the White House.

“It is absolutely shameful to see the media blocking the positive message that President Trump is trying to share with the country,” Trump campaign Executive Director Michael Glassner said in a statement. “It’s clear that CNN is trying to silence our voice and censor our free speech because it doesn’t fit their narrative.”

CNN, however, said its decision not to air the Trump ad came down to simple editorial discretion.

“CNN requested that the advertiser remove the false graphic that says the mainstream media is ‘fake news,’” the network said in a statement issued from its public relations Twitter account. “The mainstream media is not fake news, and therefore the ad is false. Per out policy, it will be accepted only if that graphic is deleted. Those are the facts.”

In response to the Donald J. Trump for President campaign’s accusations of ad censorship: pic.twitter.com/0Rbanpf0dn — CNN Communications (@CNNPR) May 2, 2017

At issue is a one-second portion of the 30-second video which shows the words “Fake News” in red letters over a five-way split-screen of various media personalities: CNN’s Wolf Blitzer, MSNBC’s Andrea Mitchell and Rachel Maddow, ABC’s George Stephanopolous and CBS’ Scott Pelley. The rest of the ad shows clips, such as Trump signing executive orders and Supreme Court Justice Neil Gorsuch being sworn in, as overlays tout gains in jobs, reductions in regulations and other legislative victories.

Trump has had an, at best, uneasy relationship with CNN, a network he’s frequently referred to as “fake news” – and once even downgraded to “very fake news” during a presidential news conference. Trump and White House Press Secretary Sean Spicer have also engaged in numerous contentious back-and-forths with CNN correspondents.