Puppycow
Penultimate Amazing
Read the article. As long as he doesn't accept the royalties, it should be legal.
Looking for more info on how common this practice is, I found this:
https://newrepublic.com/article/123156/why-did-ted-cruz-spend-122000-his-own-books
The biggest eye-opener in this one to me at least was this:
In 2011, the government’s online procurement database revealed that the State Department had spent over $70,000 purchasing copies of President Obama’s books to be used as Christmas gifts and to stock foreign embassies, including $40,000 worth of Dreams From My Father for the U.S. embassy in Cairo. This equates to several thousand copies earmarked for that single embassy.