MSNBC and CNN do not keep each other in check, it's a race to the bottom of pure garbage "journalism", which is most often either exaggerated clickbait or totally fabricated yellow journalism.

They also all participate in laundering of fake news. One of them throws up a totally false story and all of the others repeat it.

As a recent high-profile example, Washington Post falsely claimed that Trump told a Georgia election official to "find the votes", which a later leaked recording proved to be absolutely fabricated (they retracted it). CNN, MSNBC, BBC and other ethically bankrupt organisations printed the lie verbatim.