I think Josh Marshall has this figured out quite nicely:
Let’s assume for the moment that this plays out with some mix of poor judgment and perhaps bias at lower levels of the IRS but no direction from on high that would implicate the administration or top appointees themselves. The nature of this scandal - the government, particularly the IRS singling out and persecuting conservatives - appeals to the heart of the right-wing conspiracy-generating mindset.
If you wanted create a scandal to have maximal appeal to GOP base freakout, this is it. And it has the additional advantage of not creating the same sort of off-putting crazy as hitting other bugaboos beloved by base Republicans. It’s not about Obama’s ties to the Muslim brotherhood or his foreign birth. It’s about taxes, something everyone has an experience with and understands. And it’s at least rooted in something that’s true. Something really did happen. And it’s not good. It shouldn’t happen. It even has unexpected knock-on effects like the IRS’s supposed connection to the dreaded ‘Obamacare’.
That’s why you’re seeing Mitch McConnell go so full bore on this. He’s not particularly well-liked in his state and he’s not particularly well liked by Tea Parties or base Republicans. But now he can bang the drum on something that appeals deeply to these folks. He can now be with them cheek and jowl. And that is a very, very big deal. As can basically every other national Republican elected official. And again, all of this applies even if, as I assume, we learn that none of this stemmed from political hanky-panky from administration leaders.