A new AT&T merger unwinds a previous one

Over the weekend, a massive merger agreement was hammered out between telecom giant AT&T and entertainment company Discovery Inc. If it receives the blessing of federal regulators, AT&T will spin off its WarnerMedia unit—which includes CNN, HBO, and other assets—into a separate company that it will co-own with Discovery. The usual descriptions followed: it was a merger made in heaven (Discovery chief executive David Zaslav said the two “fit together like a glove”), with numerous synergies,...