If we still had a half-dozen major largely reliable news outlets that may have had some political leanings, but could still be (hah) trusted to largely report truth, rather than crafting narratives to maximize profit, it would have been much harder for the lies to spread.
The myriad effects of deregulation and massive consolidation that have cascaded in the past ~40 years (fewer companies owned by wealthier people, the destruction of local news, the erosion of norms protecting journalistic integrity, etc) are, IMO, very clearly hugely to blame for the modern state of political discourse. I'm not saying the internet didn't have an effect—it could hardly fail to; it's an enormous change in our world overall—but I have a very hard time seeing it as being more detrimental than these changes in how media companies operate.