The 1996 Illegal Immigration Reform and Immigrant Responsibility Act (IIRIRA) was a momentous law that recast undocumented immigration as a crime and fused immigration enforcement with crime control (García Hernández 2016; Lind 2016). Among its most controversial provisions, the law expanded the crimes, broadly defined, for which immigrants could be deported and legal permanent residency status revoked. The law instituted fast-track deportations and mandatory detention for immigrants with convictions. It restricted access to relief from deportation. It constrained the review of immigration court decisions and imposed barriers for filing class action lawsuits against the former US Immigration and Naturalization Service (INS). It provided for the development of biometric technologies to track “criminal aliens” and authorized the former INS to deputize state and local police and sheriff's departments to enforce immigration law (Guttentag 1997a; Migration News 1997a, 1997b, 1997c; Taylor 1997). In short, it put into law many of the punitive provisions associated with the criminalization of migration today. Legal scholars have documented the critical role that IIRIRA played in fundamentally transforming immigration enforcement, laying the groundwork for an emerging field of “crimmigration” (Morris 1997; Morawetz 1998, 2000; Kanstroom 2000; Miller 2003; Welch 2003; Stumpf 2006). These studies challenged the law's deportation and mandatory detention provisions, as well as its constraints on judicial review. And they exposed the law's widespread consequences, namely the deportations that ensued and the disproportionate impact of IIRIRA's enforcement measures on immigrants with longstanding ties to the United States (ABA 2004). Less is known about what drove IIRIRA's criminal provisions or how immigration came to be viewed through a lens of criminality in the first place. Scholars have mostly looked within the immigration policy arena for answers, focusing on immigration reform and the “new nativism” that peaked in the early nineties (Perea 1997; Jacobson 2008). Some studies have focused on interest group competition, particularly immigration restrictionists’ prohibitions on welfare benefits, while others have examined constructions of immigrants as a social threat (Chavez 2001; Nevins 2002, 2010; Newton 2008; Tichenor 2009; Bosworth and Kaufman 2011; Zatz and Rodriguez 2015). Surprisingly few studies have stepped outside the immigration policy arena to examine the role of crime politics and the policies of mass incarceration. Of these, scholars suggest that IIRIRA's most punitive provisions stem from a “new penology” in the criminal justice system, characterized by discourses and practices designed to predict dangerousness and to manage risk (Feeley and Simon 1992; Miller 2003; Stumpf 2006; Welch 2012). Yet historical connections between the punitive turn in the criminal justice and immigration systems have yet to be disentangled and laid bare. Certainly, nativist fears about unauthorized migration, national security, and demographic change were important factors shaping IIRIRA's criminal provisions, but this article argues that the crime politics advanced by the Republican Party (or the “Grand Old Party,” GOP) and the Democratic Party also played an undeniable and understudied role. The first part of the analysis examines policies of mass incarceration and the crime politics of the GOP under the Reagan administration. The second half focuses on the crime politics of the Democratic Party that recast undocumented migration as a crime and culminated in passage of IIRIRA under the Clinton administration. IIRIRA's criminal provisions continue to shape debates on the relationship between immigration and crime, the crimes that should provide grounds for expulsion from the United States, and the use of detention in deportation proceedings for those with criminal convictions. This essay considers the ways in which the War on Crime — specifically the failed mass incarceration policies — reshaped the immigration debate. It sheds light on the understudied role that crime politics of the GOP and the Democratic Party played in shaping IIRIRA — specifically its criminal provisions, which linked unauthorized migration with criminality, and fundamentally restructured immigration enforcement and infused it with the resources necessary to track, detain, and deport broad categories of immigrants, not just those with convictions.