The Republican plan is actually a 5% cut to the Supplemental Nutrition Assistance Program (SNAP, commonly known as food stamps), up from the 2.5% cut they were seeking previously.

Krugman seems to have taken the $40 billion in cuts that Republicans are proposing over a 10-year budget window and mistakenly applied them to a single year — thus turning a 5% cut into 50%.

Krugman may have missed this because he’s been misled by his own paper’s coverage of the issue. He links to an August 1 Times article about the new Republican proposal, which has a headline saying Republicans want to “Slash Food Stamps,” and which doesn’t provide the context that the $40 billion cut would be off a spending baseline of about $780 billion.