The basic purpose of this book is to help save the Republican Party from self-destruction. As a liberal, I'm not terribly invested in this goal, but I read the book anyway, because Matt Lewis is one of my favorite conservative political writers and I was interested in hearing his take on the party's problems.
As far as the diagnoses goes, Lewis is basically on-point. He accurately notes that the Republican Party has given outsized power to some of the most destructive elements within the conservative movement, which I'd broadly describe as Tea Party-type agitators (Sarah Palin, talk radio hosts, etc) anti-intellectuals, and new converts to conservatism who aren't informed about how the movements history or how the political process works. Lewis is also correct that demographic trends are working against the GOP, and that this will be the party's undoing unless it can make itself more appealing to growing demographics (that is, non-rural non-whites).
The most interesting part of the book to me was the section on culture. Lewis's basic premise is that politics (by which he means both laws and political attitudes) follows cultural trends, not the other way around, and that cultural trends, in turn, are influenced by things like entertainment and pop culture. Lewis points out that, while social conservatives have done a good job getting themselves and their allies elected, they've done a terrible job of changing cultural attitudes in their direction (gay marriage being a prime example), and as such, they're not able to effectively enact their ideologies. He suggests that conservatives focus on infiltrating mainstream entertainment and pop culture, and I found this to be a fascinating argument.
Lewis's diagnoses of the problems are spot on, but his prescription is a bit wanting. He says the Republican Party should enact some manner of immigration reform as a way of wooing Hispanic voters. The thing is, "immigration reform" is a vague term that can refer to either very liberal or very conservative policies. Though he doesn't say it, Lewis is clearly referring to liberal reforms (otherwise, they'd hold no appeal to Hispanic voters), yet he knows that the mere suggestion of things like amnesty or a path to citizenship are a non-starter for the vast majority of Republican lawmakers, and so he doesn't specify what type of "immigration reform" the GOP should or could pass.
But this has been the central problem facing the GOP for years: How to pass immigration reform that's both amenable to GOP lawmakers (and by extension, base voters) and also appealing to Hispanics. There is just no evidence that this is possible, as evidenced by the absolute failure of the party's attempts at immigration reform in 2014, and Lewis hasn't proposed a specific solution for fixing this impasse. To be fair to him, I'm not sure there is one.
In one section of the book, he correctly notes that there's a tension between the short-term goals of Republican campaign managers (they want to win individual elections) and the long-term needs of the party (it needs to expand the party's appeal or face destruction). What this basically means is that the GOP is pandering to rural, white voters at the expense of everyone else, because this is a winning formula for many legislative and gubernatorial elections. But it's not a winning strategy for winning the presidency.
Again, this is a good observation, but I'm not sure the problem can be as easily overcome as Lewis suggests. This conflict of interest within the party has played out over the course of several election cycles, and the fact that the GOP is on the cusp of nominating Donald Trump — who exacerbates this problem moreso than any other Republican candidate I can imagine — suggests that the party is not inclined to think long-term, and will instead focus on short-term successes at the expense of the party's general health.
I could be wrong about this, but I'm starting to think the Republican Party might need to sacrifice this presidential election, and perhaps the next one, in order to reform itself. That was my biggest takeaway from this book, because all of the problems Lewis describes have been pretty apparent for quite some time now. His proposals are all good ones, but there's no indication that the powers-that-be in the Republican Party have any inclination to adopt them.
However, Lewis may be on to something by proposing that conservatives focus, for the time being, more on changing cultural attitudes than changing laws, because that's how you actually built long-term ideological support for your policies. The GOP might as well try something new, because what it's been doing for the last several decades clearly isn't working.