It tanked the polls for GOP congress. What helped in 2014 mid-terms the most was the TV pictures of illegal children flooding in, IMO. Also helped increasing unpopularity of Obamacare as more people are finding out how it has affected them.
When the employer mandate goes into effect next year, that can only help republicans in 2016.
The only real poll is an election. The GOP did not hurt itself with the government shutdown over Obamacare.