Why was Trump's run in 2016 treated seriously by the media, even from when he announced?

[Fuzzy Bear]

Firstly, the press had been taking Donald Trump seriously as a potential Presidential candidate since 2000.  They took him seriously as a possible Reform Party nominee.  They took him seriously in 2012.  

In 2015-16, Trump positioned himself in a unique niche; he was a candidate who took a number of regular GOP positions, but some other positions that challenged orthodoxy, particularly the orthodoxy of Free Trade and perpetual involvement in foreign wars that (A) were viewed as wrongheaded by many and (B) seemed to be conducted with no clear objective in mind and no vision of what victory would be.  These were policies that the Bushes, Dick Cheney, and a slew of other Republicans (Romney, Huntsman, Ryan, and the Congressional GOP Establishment) were vested in.

In doing so, Trump mobilized a force in the GOP that had been somewhat shoved to the side; the Ross Perot voters.  These voters had been long written off, but they were a traditional Republican constituency, and they were joined with voters who were once Democrats whose jobs were being eliminated by the Democratic Party's new "Green" orientation.  Indeed, Trump's entry into the race engineered a real political realignment that is still sorting itself out today.

The press is supposed to take such events seriously.  The press's job is not to manipulate the public to support the choice of the Democratic Party; it is to present the issues before the people.  The idea that Donald Trump should not be treated seriously as a Presidential candidate is laughable, whether you agree with his agenda or not.