He proclaimed this was "a deal we will not approve in my administration, because it's too much concentration of power in the hands of too few."
For good measure, Trump called for undoing Comcast's purchase of NBC, completed three years ago, also because it created a media conglomerate involving a network whose coverage Trump deems unfair to him or, as he put it, is "trying to poison the mind of the American voter."
To be sure, mega-mergers are never particularly popular, and they often pose legitimate antitrust concerns.
Trump was hardly the only politico to sound an alarm about the proposed AT&T-Time Warner deal.
Senator Bernie Sanders took a break from campaigning for Hillary Clinton to call on the Obama administration to "kill" it. Senator Al Franken, like Trump a former NBC television star, said he was "sceptical" of the deal, because mergers "can lead to higher costs, fewer choices and even worse service for consumers."
Of the three politicians, only Trump is running for president, which means only he would be in a position to appoint the executive-branch officials who must actually decide whether to seek to block the merger.
Even Franken appropriately said he wanted more information before reaching a final conclusion. In short, Trump prejudged the issue in a way that could have real-world consequences - in the form of less due process and rule of law.
In fact, it is too early to assess the merits of the deal.
AT&T's avowed goal is a vertically integrated company capable of producing news and entertainment content and transmitting it via its own wireless technology.
This might indeed reduce consumer choice if the merged firm tried to hinder competing content providers' access to its network, something AT&T says it has no interest in doing.
Alternatively, it could enhance choice if the net effect were to disrupt cable providers' local market power.
The responsible approach, for a presidential candidate, is to express concern about the market power the merged company might wield, while acknowledging that there is still a lot we don't know and urging regulators to scrub the merger thoroughly before granting approval - if they do.
That's the stance taken by Clinton's campaign.
