Fact check: Mostly true. The New York Times predicted that Donald Trump would lose the general election, even up through election night. While they were accurate towards the end of the primary on Trump, they admitted to underestimating him throughout the process.
Fact check: False. There was no form of an apology in the letter Donald Trump is referring to in that tweet. A Trump spokesman said the letter refers to an admission that they underestimated Trump's chances at winning.
...dwindling subscribers and readers.They got me wrong right from the beginning and still have not changed course, and never will. DISHONEST — Donald J. Trump (@realDonaldTrump) January 28, 2017
Fact check on "dwindling subscribers and readers": False. The New York Times added over 130,000 subscribers within a month after Donald Trump's election. The Washington Post broke its own traffic records in October, reaching almost 100 million monthly unique visitors.
Something we're watching: This is all part of Donald Trump's media manipulation playbook. He's used this exact attack before, shortly after he was elected.