Someone at MSNBC Told Another Person At MSNBC That Someone Not At MSNBC Told Them That Tom Steyer Is Dropping Out. Then That Person (The Second MSNBC Person) Tweeted It.

Just breaking on @MSNBC: Tom Steyer is ending his presidential campaign.
— Kyle Griffin (@kylegriffin1) March 1, 2020

By the actual wording of this tweet, I confess that it is possible that the second MSNBC employee actually literally saw the report from the first MSNBC employee while watching MSNBC.
Update: According to some other people on Twitter, Steyer has now in fact dropped out.
Update 1.5: MSNBC does not have a Roku app, and it makes it very hard to watch MSNBC when you are home on a Saturday night trying to follow the news.  Just something to think about, MSNBC.