Since the start of the Democratic National Convention, ratings have exploded for the cable news channel MSNBC.

So have tensions among the network's top anchors.

The convention was supposed to be the network's coming-out party as a hub for politics. But a year of programming and personnel changes have led to behind-the-scenes strain, which bubbled to the surface repeatedly this week in open arguments between hosts.

In an uncomfortable moment Tuesday night, an exhausted-looking "Hardball" host Chris Matthews shouted at a producer ("I'll wrap in a second!") before a stilted exchange with "Countdown" host Keith Olbermann, in which the two argued about who was talking out of turn. Mr. Olbermann made a flapping-lips hand gesture, and Mr. Matthews took umbrage. House Majority Leader Steny Hoyer sat quietly on-screen, waiting to be interviewed.

That incident followed a seven-minute back-and-forth Tuesday afternoon between "Morning Joe" host Joe Scarborough and network correspondent David Shuster. Mr. Scarborough, a former Republican representative from Florida, accused Mr. Shuster, a registered independent, of taking a "cheap shot" by mentioning his party affiliation. Mr. Scarborough sarcastically added: "I feel so comforted by the fact that you're an independent. I bet everyone at MSNBC has 'independent' on their voting cards."