Unfortunately truth is hard to come by anymore, especially with social media and extreme partisanship. We have been divided as a nation worse than ever before, and people in high positions are now taking advantage of this. They are very quick to spread false stories and spread hate, and too few people are bothering to research the truth.
It isn't only "PizzaGate" that shows the Conservatives no longer care about the truth, the whole 2016 election campaign was thought by the Conservatives using massive lies and their followers believing it. I also think the question of "is the truth becoming irrelevant" would be better as "why is the truth now irrelevant to Conservatives" because we all know they have zero interest in the truth right now, there is no "becoming" about it.
In any political battle, both sides of the argument sling insults and false claims at their opposition. It is impossible to say that truth is irrelevant to conservatives in the same way that it is impossible to say that truth is irrelevant to liberals. Not only is truth difficult to define in a political sense, but what each individual views to be truth is their guideline for all decision making.
People know the difference between real and fake news. The whole reason Fox News even started, and then the Drudge Report, is because people wanted a forum to find the news. People are smart enough to judge for themselves what is and isn't real. Conservatives want to see the truth, not have liberal news outlets tell them what to believe.