Well researched article. While the authors don't belabor the point, I think people who have paid attention to the timeline know that this is the key sentence:
Some election lawyers said they believed a wave of lawsuits against the I.R.S. and intensifying Congressional criticism of its handling of applications were intended in part to derail those audits, giving political nonprofit organizations a freer hand during the 2014 campaign.
http://www.nytimes.com/...