Although the nine Supreme court justices are sitting in the front pew, Justice Mendoza whom Bartlet appointed is not one of them.
In his meeting with Leo, Sam mentions that the Democratic candidate in Texas' 22nd Congressional District was "an electrical engineer who paid his filing fee by dumping the cash out of a cigar box. However, a few episodes earlier, "20 Hours in America: Part I," Bartlet is introduced to the newly-elected Democratic congressman from Texas' 22nd Congressional District, Peter Lien.
During the Red Mass, Vivaldi's Gloria is sung by the choir as a processional. However, in a Catholic service (like the Red Mass) the Gloria has a fixed place during the mass (after the Kyrie) and would never be used as a processional.
CJ tells the press corps that the Red Mass will take place at the Basilica of the National Shrine of the Immaculate Conception. The actual Red Mass takes place at the Cathedral of St. Matthew the Apostle.
The Red Mass is mentioned as a possible First Amendment issue. It is not. Politicians are invited to the Red Mass, which is held by a private church, but they are not required to attend.