It's not the partisanship that's causing the problem, it's the business model.

Investigative journalism, done properly, takes time and money. And it produces long articles that can be challenging to read and involve the detail that backs the claim. In a clickbait world, this doesn't produce profit.

There's no functioning business model for it now, but we have built our democratic systems on the assumption that there is. Rich folks buying newspapers and then meddling with their editorial policy was always a problem, but with the editorial office completely dependent on the rich folks for their salaries it gets harder to resist.