Few 'textbook' texts with chapters on foundations, behavior, institutions, etc. from 'radical' perspective, guess the 'market' has spoken! Of handful of such books over last 25 years, they are either out of print or haven't been revised for a while (although you might check for updates). Examples include: Michael Parenti, _Democracy for the Few_ Edward Greenberg, _The American Political System: A Radical Approach_ Kenneth Dolbeare & Murray Edelman, _American Politics: Policies, Power and Change_ Ira Katznelson & Mark Kesselman, _The Politics of Power: A Critical Introduction to American Government_ Daniel Hellinger & Dennis Judd, _The Democratic Facade_ Lewis Lipsitz & David Speak, _American Democracy_ Lucius Barker & Mack Jones, _African Americans and The American Political System Harrell Rodgers & Michael Harrington, _Unfinished Democracy: The American Political System John Harrigan, _Empty Dreams, Empty Pockets: Class and Bias in American Politics
An 'older' leftish text released in new ed. this year is Robert Sherrill's _Why They Call It Politics: A Guide to America's Government_.
Critical (to varying degrees) textbooks released in last couple of years include: Todd Swanstrom, Bruce Miroff, and Ray Seidelman, _The Democratic Debate_ Edward Greenberg and Benjamin Page, _The Struggle for Democracy_ Theodore Lowi, Benjamin Ginsberg & Margaret Weir, _We the People_
Beyond above, there is swamp of mainstream texts that are pretty much interchangeable although two that are pretty good from liberal feminist perspective are: Susan Welch, John Gruhl, John Comer, Susan Rigdon, Jan Vermeer, _Understanding American Government_ Karen O'Connor & Larry Sabato, _American Government: Continuity & Change_
My current fave mainstream intro US gov't text: Joseph Melusky, _The American Political System: An Owner's Manual_ Melusky book comes packaged as would a car owner's manual and even includes a warranty message: Congratulations on being a citizen/owner of the American political system! Your system is covered by lifetime warranty. However, some maintenance is required. *Never leave this system unattended. Pay attention to the actions of the public officials who operate the system on your behalf. *This system requires close supervision. Provide public officials with instructions, notify them of your displeasure, and take corrective measures on election day and at other times if necessary. *Never use this system while drowsy or while under the influence of drugs or alcohol. *Use this system only for its intended purposes as described in this manual. Please read this manual carefully for information about how this system operates and how it was designed to operate. *This system is a democratic one. It will not operate properly if you "unplug" it through neglect. *Failure to read the owner's manual will result in less-than- satisfactory performance. Failure to supply routine maintenance will void the warranty.
I kid you not, Michael Hoover