Sarah Duggin, professor, law, was quoted in a politifact story on presidents enforcing laws.
... The idea that a president may not enforce the law sounds odd, but the legal experts we talked to said it was common.
"As a practical matter, there is little doubt that the president sets law enforcement priorities, and that some laws will be vigorously enforced and others will not," said Sarah Duggin, a professor at the Columbus School of Law. "It is also true that at various times in our history, presidents have declined to enforce laws they deemed unconstitutional." ...
Continue reading in Politifact.