Do columnists like Krugman repeat themselves?

Ok, not that many op-ed pieces of mine have been published. Despite that, a couple of months ago I scanned through some of them to see if I have used any phrases verbatim. I was relieved that I hadn't.

Why this remark? Well, I was reading Krugman's latest column, and came across this sentence there: And as Upton Sinclair pointed out, it’s hard to get a man to understand something when his salary — or, we might add, his campaign war chest — depends on his not understanding it.
I was sure I had seen it somewhere else in his writings. I remembered it only because I spent a few minutes what exatcly Sinclair was meaning, and what the context might have been. Anyway, a Google search later I located Krugman's earlier usage. But, it was not in a column; it was in his blog.