The IRS isn't going anywhere, and there isn't going to be any huge political fallout from this like some people are sitting at home fapping about.
If anything, it's going to be used as a jumping off point for both sides to re-introduce campaign finance reform into the discussion. There is plenty of support on either side of the aisle for this, and if the Republicans were smart, they wouldn't focus on trying to tie this to individual Senate races, because the details will largely be forgotten about. Rather, they'd be better off introducing and taking the lead on bi-partisan legislation to reform the system, and then benefit from the goodwill that creates, which translates into votes.
Smear campaigns rarely work over the long-term, but reform is something everyone likes to get behind, D or R, and something every politician likes to take credit for, D or R.