This is a "love it or hate it" book; there's no middle ground. Having read it I can see that those of the liberal persuasion will detest the book, while those of a more conservative inclination will really like it. As one who tends to the more conservative side of the political spectrum, I will confess that I enjoyed the book very much, even though at times it seemed "over the top".
This is a tale wherein the "good guys" are the Texans and those who believe in and stand up for the Constitution, and the "bad guys" are the Washington bureaucrats and administration officials who see no problem in disregarding the parts of the Constitution that they don't like.
When the liberal president is the target of an assassination, even though the government and White House officials know the truth about the would-be killer, they deliberately announce that he was a member of the Tea Party, and that sets off a whole chain of awful and unbelievable events. Riots, burnings, looting and killing in major cities, and a "witch hunt" for all Tea Party members, who are arrested without cause, not given their Miranda rights, and held in secret places where even their families cannot find them.
Into this crisis steps the Governor of Texas and the Texas Rangers, who set out to rescue the wrongfully imprisoned Tea Party members, and defy the Federal government for its overreaching powers of arrest, etc.. It gets tense, and there are more confrontations, killings, and such, until the end, where the author posits an interesting solution to the problem of a rogue government riding roughshod over its citizens.
To those who say this is totally unbelievable and can't happen here, I only need point to today's news, with the IRS harassing conservative groups, a stonewalling on what really happened at Benghazi, and most chilling of all, the secret grab by the government of private phone records of reporters, and a veiled accusation of `conspirator" against a member of Fox News.
This isn't the first book to imagine an American government out of control. For those who are interested, I recommend reading "It Can't Happen Here" by Sinclair Lewis. It was written in the 1930s, but it's still a chilling account of what might occur when a government group at the top decides that they know better than the people they are supposed to be serving, and that they, and only they, have the right to do what they will, because they are the only folks who have the right ideas.