The Boston Globe invited newspapers across the country to stand up for the press with editorials on Thursday, and several began appearing online a day earlier.
Nearly 350 news organisations have pledged to participate, according to Marjorie Pritchard, op-ed editor at the Globe.
In St Louis, the Post-Dispatch called journalists “the truest of patriots”, while the Chicago Sun-Times said it believes most Americans know Mr Trump is talking nonsense.
The Globe editorial board called for an end to President Trump’s sustained assault on the #FreePress. Hundreds of publishers around the US answered that call https://t.co/XpgjyrODMp pic.twitter.com/7lnSTlE6Sh
— The Boston Globe (@BostonGlobe) August 15, 2018
The Fayetteville Observer said it hopes Mr Trump will stop making such accusations, “but we’re not holding our breath”.
The North Carolina newspaper added: “Rather, we hope all the president’s supporters will recognise what he’s doing – manipulating reality to get what he wants.”
Some newspapers used history lessons to state their case. The Elizabethtown Advocate in Pennsylvania compared free press in the United States to such rights promised but not delivered in the former Soviet Union.
The New York Times added a pitch.
“If you haven’t already, please subscribe to your local papers,” said the Times, whose opinion section also summarised other editorials across the country.
“Praise them when you think they’ve done a good job and criticise them when you think they could do better. We’re all in this together.”
That last sentiment made some journalists skittish. The Wall Street Journal, which said it was not participating, noted in a column by James Freeman that the Globe’s effort ran counter to the independence that editorial boards claim to seek.
Mr Freeman wrote that the president has the right to free speech as much as his media adversaries.