There are many voices at the table when it comes to interpreting changes to immigration law. However, understanding the practice material will better prepare any person willing to practice in the field of immigration.
After the Supreme Court’s decision in Mathis v. United States, 136 S. Ct. 2242 (2016), courts continue to grapple with two approaches:
CATEGORICAL APPROACH
Is the method for determining whether an offense (generally a prior conviction) fits within a given definition, such as for “crime of violence” “drug trafficking offense” “violent felony” or other similar terms. To do so, the court must compare the elements of the prior offense to the relevant definition. Under the categorical approach, courts are not permitted to look to the conduct underlying the prior conviction, only to the statute of conviction, to determine the elements of the prior offense.
MODIFIED CATEGORICAL APPROACH
Similar to the categorical approach, the modified categorical approach is used to determine whether an offense (generally a prior conviction) fits within a given definition, such as for “crime of violence” “violent felony” or similar term. The court must compare the elements of the offense of conviction to the relevant definition. Under the modified approach, the court may use certain additional documents, such as a charging document or plea agreement from the prior conviction, to determine the elements of the offense of conviction.
**SEE https://www.ussc.gov/sites/default/files/pdf/training/annual-national-training-seminar/2016/backgrounder_categorical-approach.pdf for further clarification on the Categorical and Modified Categorical Approach.
CHEVRON DEFERENCE
Chevron deference is a principle of administrative law requiring courts to defer to interpretations of statutes made by those government agencies charged with enforcing them unless such interpretations are unreasonable. The principle is named for the 1984 Supreme Court case Chevron U.S.A., Inc. v. Natural Resources Defense Council, Inc., which involved a dispute over the Environmental Protection Agency’s interpretation of a provision of the Clean Air Act Amendments of 1977. Under Chevron, even if a court finds that another interpretation is reasonable, or even better than the agency’s interpretation, it must defer to the agency’s reasonable interpretation.
Generally, to be accorded Chevron deference, the agency’s interpretation of an ambiguous statute must be permissible, which the court has defined to mean “rational” or “reasonable.” In determining the reasonableness of a particular construction of a statute by the agency, the age of that administrative interpretation as well as the congressional action or inaction in response to that interpretation at issue can be a useful guide, if the Congress was aware of the interpretation when it acted or refrained from action, and when the agency’s interpretation is not inconsistent with the clear statutory language.
See the links below for further clarification on the Chevron Deference
Essentials of Immigration Law by 
Immigration & Nationality Act 2016 Ed. by 
Kurzban's Immigration Law Sourcebook by 