History is a proper subject for a forum, not a thread. If you want to talk about political journalism in the U.S., it has been going on since the earliest days of the republic. However, it had not spilled over into historical journalism until the 1940s, when Joseph Kennedy decided to rehabilitate his pre-WW2 appeasement statements about Nazi Germany in order to promote the political careers of his sons.
As a result, JFK's wartime misdeeds (dating a Nazi spy in Hawaii and allowing his PT boat to be sunk) have purged from the historical record, as have his fraudulent political campaigns and secret deals with Krushchev during the so-called Cuban Missile Crisis. This continued with the historical misrepresentation of the Watergate "scandal" and suppression of the Clintons' crooked political and business dealings. The final corruption of historical journalism began with the Presidential candidacy of Barack Obama, whose election was considered such an important event as to warrant the complete abolition of critical journalistic reporting. This trend has continued with the election of Donald Trump, albeit with an opposite motivation.
Ironically, this corruption is finally sowing the seeds of its own demise. Modern journalist/historians have proven themselves to be so biased that their opinions are largely ignored. Good for them.