Mr. Issa has relished making this investigation a political fight. Last week, he seemed to bait Mr. Holder when he said in a statement, “the Obama administration has not asserted executive privilege or any other valid privilege,” so it could not refuse to produce the materials.

On Wednesday, for the first time since he was elected, President Obama invoked executive privilege on the disputed documents. Doing so now bars prosecution of Mr. Holder in federal court should the full House vote to hold him in contempt of Congress.

Executive privilege cannot and should not be allowed to shield the executive branch from regular, valuable Congressional oversight. There was no reason the House committee and the Justice Department could not work out a deal to produce the documents requested, or some form of them. Instead, they show again that every issue, large or small, can be turned into ammunition for political combat.