It is the third time that the Vatican has rejected the US candidate to serve as ambassador there according to the Washington Times. Cf. http://washingtontimes.com/news/2009/apr/07/embassy-row-7410554/ The Pope has done this because all the candidates were pro-abortion.
It seems that the US administration is trying to force in these unsavory characters to make a point that the Vatican will condone the reality of abortion i.e. that there is some tolerance allowable in this matter. Little did they know that the Church is guided by God's Holy Spirit and will not be suckered into supporting godless policies and compromises with evil.
Then again, there is also a possibility that Washington is misled by the Catholic pols who present an obscene interpretation of the Church's position as allowing some form of lesser-evil. This may have been further corroborated by the refusal of Archbishops Wuerl and Bishop Loverde to enforce the Church law that will exclude pro-abortion pols from Holy Communion.
Regardless, what matters is the direction from the top and there is no confusion there, no room for doubt as the Holy See demonstrates the unity and integrity of belief and life not only at a personal level but also at the state level.