He is not saying that anyone, not even the priest, is to judge the state of a persons soul. He said that if AFTER personally counseling the person regarding his/her position, the politician did not change his/her position he would tell the politician not to present him/herself for Communion. If AFTER both counseling and being told not to present him/herself for Communion, the politician still insisted on presenting him/herself for Communion, he/she should be denied.
The politician is not being denied because he/she is in a state of sin (yes, he/she could have just been to Confession) but rather because he/she is making a public scandal out of our most precious Sacrament. This is not really different from the decision of many bishops to deny Communion to the Rainbow Sash bunch who show up at Pentacost. They are coming to Communion in an unworthy manner (not necessarity an unworthy state) and are denied.