It's impossible to claim copyright on published government words, because they by definition belong to the public. We pay for 'em. Yet, one can plaigerize them by improper or absent citation of the government source, which is also a criminal matter.

If a non-government author has used government documents in his work, cited properly and edited to his specifications, and is then quoted, especially at length, without attribution, that's a violation of his copyright because the editorial process is also his intellectual property.

This is law, folks, not rocket science. It's a different world. Please play it safe: reproduce less than 10% of anything, never the "heart of the work" (a legal term in copyright law); use quotation marks or Robert's blockquote HTML tags; cite the work properly; and if at all possible, link to the complete article. You will thus be in compliance with "fair use", which allows for limited quotation of published works for scholarly or critical purposes. The criticism only needs to be professional; it doesn't have to be favorable.

I think the section in the Zone's User's Guide on copyright is still current. It goes into much more detail than the Cliff's Notes version here. If any of the links are dead, I'll see to it.