We use the indefinite article before a proper noun sometimes when we want to show that we are seeing a specific aspect of that noun.
It was a very dirty Alex who came out of the cave. (Alex is not usually dirty, but got dirty in the cave.)
A very happy Alice greeted us to tell us about her engagement. (Alice was very happy.)
In this case, the White House (meaning the Obama administration) had been the subject of criticism.
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