Union & double imputation

For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God. (2 Corinthians 5:21)

I believe the writings of John Murray enabled me to grasp firmly the doctrine of double imputation: Christ's righteousness is accounted to us, and our sin is accounted to Christ. In the last few years, James Jordan has on any number of occasions asserted that this doctrine is not in the Westminster Standards and not required by Scripture. Whether it was originally intended to be in the Westminster Standards is open to debate, but certainly the animus imponentis of American Presbyterianism is to find it there, as is demonstrated at least as far back as A.A. Hodges' commentary on the Confession of Faith. Moreover, even if one doesn't quite find the imputation of Christ's righteousness in 2 Corinthians 5:21, it's certainly there in Romans 4:3-5. Hence, I do not understand how anyone can reject this doctrine.

At the same time, some who have made their bones in opposing the Federal Vision (in which camp is James Jordan) have also wanted to distance themselves from Calvin's emphasis on union with Christ as the font of all the benefits of redemption. Exhibit A: J.V. Fesko in the Spring 2010 issue of The Westminster Theological Journal. This, too, mystifies me, as Paul clearly tells us we are righteous not merely because of an external, forensic declaration, but because we have been united to Christ ("in him").

Recent debates in Reformed circles have caused some to lose sight of our historic points of consensus, at least as evidenced by 2 Corinthians 5:21.