Hajnal is a scholar of racial and ethnic politics, urban politics, immigration, and political behavior. Hajnal is the author of a range of books and articles on partisan politics, voter turnout, minority representation, and local spending. Hajnal has published in the American Political Science Review, the Journal of Politics, Public Opinion Quarterly, and numerous other journals, edited volumes, and newspaper editorial pages. He has received numerous honors for his research and writing including the Best Book on Race Ethnicity, the Best Book on Urban Politics, and the Best Paper on Urban Politics (all from the American Political Science Association). He has received a number of fellowships including a Center for Comparative Immigration Studies Fellowship, a Center for the Study of Democratic Politics Fellowship, and a Chris and Warren Hellman Fellowship. His research has been funded by the Russell Sage Foundation and the Andrew W. Mellon Foundation. He holds a PhD in political science from the University of Chicago. Prior to taking his position at UCSD, he served as a Research Fellow at the Public Policy Institute of California and as a legislative assistant in Canadian Parliament.
Argues that voter identification laws decrease minority turnout in American elections. Discusses how voter turnout among whites does not change, but turnout among Hispanics, Blacks, Asian Americans, and liberals falls by several percentage points when states require citizens to show identification in order to vote.