His newest book,A Lethal Obsession: Anti-Semitism from Antiquity to the Global Jihad just came out last month. It's more than a thousand pages long. The other day I saw a copy, and you wouldn't wish it to fall on your toe.
In spite of the title, it apparently focuses not on the longevity of Jew hatred, but on its post-Holocaust vitality. Anyone who wishes to speak with authority on this topic, must read the book, even though it will take a bit of effort. That's how one acquires authority: by working at it.
If you'd like to know about the thesis without the major effort, here's a fine review by Jeffrey Herf. (h/t Silke)
When Hitler made his famous threat to exterminate Europe’s Jews in 1939, many Western political observers did not believe he meant what he said. It was too incredible and without precedent. No political leader before had so bluntly and publicly announced his intention to engage in mass murder. And so the disgust that greeted Hitler was mixed with disbelief. But the leaders of our own time do not have the excuse of incredulity. As much as any historian can, Robert Wistrich has documented the fact that radical anti-Semitism is in earnest, that its geographic and cultural center of gravity has shifted, and that it has again become a factor in world politics. The advocates of this disgusting doctrine have the power from which to make good on their threats.