After Donald Trump was convicted last week in his hush-money trial, Republican leaders wasted no time in rallying behind him. There was no chance the Republican Party was going to replace Trump as their nominee at this point. Trump has essentially taken over the G.O.P.; his daughter-in-law is even co-chair of the Republican National Committee. How did the Republican Party get so weak that it could fall victim to a hostile takeover? Daniel Schlozman and Sam Rosenfeld are the authors of “The Hollow Parties: The Many Pasts and Disordered Present of American Party Politics,” which traces how both major political parties have been “hollowed out” over the decades, transforming once-powerful gatekeeping institutions into mere vessels for the ideologies of specific candidates. And they argue that this change has been perilous for our democracy. In this conversation, we discuss how the power of the parties has been gradually chipped away; why the Republican Party became less ideological and more geared around conflict; the merits of a stronger party system; and more.