WASHINGTON — The Trump administration’s decision to impose tariffs on Canadian newsprint is hastening the demise of local newspapers across the country, forcing already-struggling publications to cut staff, reduce the number of days they print and, in at least one case, shutter entirely.

Surging newsprint costs are beginning to hurt publications like The Gazette in Janesville, Wis., the hometown paper of the House speaker, Paul D. Ryan, which has long felt a mandate to punch above its weight. The paper, with a newsroom staff of 22, was the first to publish the news in 2016 that Mr. Ryan would support the presidential candidacy of Donald J. Trump. And while its editorial board has endorsed Mr. Ryan countless times, the paper made national news when it chided him for refusing to hold town halls with his constituents.

Now, with newsprint tariffs increasing annual printing costs by $740,000, The Gazette has made several cuts to its staff and is using narrower paper, reducing the number of stories published every day.

“We’re all paying a huge price,” Skip Bliss, the publisher of The Gazette, said of the tariffs’ effect on the industry. “I fear it’s going to be a very difficult time. I think there’s probably going to be some casualties.”