Which is the correct statistical operation to use to determine significance in this situation?

I'm writing a term paper for a 400-level social science research course in which I hypothesize that the Motor Voter Act increased voter registration, but not actual turnout. My ysis involves trying to show that there was no significant difference in the change in voter turnout in presidential elections after the page of the Motor Voter Act in 1993 compared to the change in turnout in the four states (MN, ND, WI, WY) that are exempt from Motor Voter because they already had registration laws that were at least as liberal as those prescribed in the act. I'm using the registration and turnout numbers for 88 and 92 (Pre MV) and comparing them to 96 and 00 (Post MV). What type of ysis (regression, correlation, chi-square, etc.) should I run and how should I set it up? Since my experimental group (46 states) is so much larger than my control group (only 4), can I switch their positions and treat the states that didn't change as the experimental group? Thanks.