The introduction and first chapter of Jerry Coyne's Why Evolution is True (WEIT) were mostly review for me, but review is good for clarifying and summarizing what one already knows. Coyne explained the basic elements of evolutionary theory – natural selection, mutation, common descent, etc. – and went over some of the general predictions that the theory makes.
Coyne starts off the book with a description of the 2005 court case Kitzmiller v. Dover, which decided whether intelligent design (ID) could be taught in public schools. The judge in the case, John E. Jones III, was a Bush-appointed Republican and fervent Christian, so if he had any biases, they were likely in favor of ID, not against it. However, in the end he ruled against ID, saying that it was clearly a religiously-motivated offshoot of creationism, and that teaching it as science would violate the First Amendment.
The ID textbook Of Pandas and People was a key piece of evidence in the case. As it turns out, Pandas was originally an explicitly creationist text, but in later revisions the term "creationism" was often replaced with "intelligent design" with no other substantial changes. A graph of this is provided below. One particularly egregious example of this, where "creationists" is changed to "cdesign proponentsists" (a typo of "design proponents") can be found here.
This is far from the only evidence that ID is just rebranded creationism, however. Most of the major ID advocates—people like William Dembski, Michael Behe and Stephen Meyer—believe the "designer" is the God of Christianity. In 1998, the Discovery Institute (the primary ID organization) privately drafted their wedge document. Their Christian motivations are displayed right on the cover with an image of Michaelangelo's painting The Creation of Adam:
But their religious agenda is laid out even more clearly in the text itself. They sought to "build up a popular base of support among our natural constituency, namely, Christians." They also intended to promote "the theistic understanding that nature and human beings are created by God." And they proudly declare that "Design theory promises to reverse the stifling dominance of the materialist worldview, and to replace it with a science consonant with Christian and theistic convictions."
With evidence like that, it's not surprising that the Discovery Institute was upset when the document was leaked. There can be no mistake: ID is a movement originating from Christian creationism, supported by Christians, seeking to advance Christianity. If it looks, swims, and quacks like a duck... well, you know the rest.