So far, I’ve found three newspapers that have published editorials calling for Trump’s resignation, the Indy Times, St. Louis Post-Dispatch, and Connecticut Post. See data viz below. Click on the newspaper name and follow the link to the actual editorials.
By the time Nixon resigned in August of 1974, most major newspapers had called for him to resign. Let’s see how things progress this time.
EDIT: It’s now four newspapers, with the addition of the Orlando Weekly.
EDIT: Lots of activity after the House hearings — now we’re up to 12, that I know of.