Kudos to The Washington Post

I was just reading the first couple of sentences in a Washington Post article by Ben Terris. The first sentence looked like this:

For half a century, the out-of-power party has used their response to the State of the Union address to capitalize on the dregs of audience left over from the president’s speech and mount their own aftershow.

There are two mistakes here. Well, the same mistake made twice. I called The Washington Post, got hold of Mr. Terris, and he readily acknowledged the mistakes, promising speedy correction.

What are the mistakes?