They absolutely want to investigate AG Garland and if they retake the House, that's exactly what they will do, as well as FBI Director Chris Wray. They'll do it because it works. We can call them sham investigations, which they are, but unfortunately, there are a lot of ignorant voters out there in the so-called moderate center.
The goal of these sham investigations like Benghazi and Fast & Furious is not necessarily to convince Americans that these investigations have merit. The aim isn't to persuade. Rather, it's to destroy confidence in the system and its institutions, so that ultimately, people don't know what to believe anymore. That's actually as much what kills functioning democracy as anything: people begin to think that the whole system is hopelessly corrupt, that their votes mean nothing, that the system can't be changed, that "the truth" can't ever really be known because everyone has an agenda (aka "both sides-ism"). So then, why bother voting? But rest assured, the faithful on the right will vote, and they will legislate to make sure it's harder for non-conservatives to vote for their candidates.