In Crackup, Samuel L. Popkin tells the story of how the Republican Party fractured into uncompromising groups with irreconcilable demands. Changes in campaign finance laws and the proliferation of mass media opened the way for newly energized groups to split the party. The 2002 "McCain-Feingold" campaign finance reform bill aimed to weaken the power of big corporations and strengthen political parties by ending corporate donations to the parties. Instead, it weakened legislative leaders and made bipartisanship toxic.

Popkin argues that moving money outside the political parties fueled the rise of single-issue advocacy groups and Super PACs funded by billionaires with pet issues. This allowed self-promoting politicians to undermine colleagues with an unprecedented use of tactics once only used to disrupt the other party. One such politician was Ted Cruz, who effectively promoted himself at the expense of the party, mobilized other obstructionists in Congress, and blocked compromises on immigration and healthcare. Into this abyss came Donald J. Trump, who took advantage of the party's inability to do anything for Republican voters struggling with economic decline.

A gripping explanation of why the GOP ended up with Trump as their standard bearer, Crackup forces us to look at the deeper forces set in motion two decades ago.