Harry was too distracted to parse the look, focused on Riddle’s ruthless pragmatism. Appalling as Harry found it, Riddle’s analysis was probably right – if he wouldn’t take anything less than a Wizengamot seat that left mainly old pureblood families, and almost all of them were too bigoted to take a poor half-blood with no connections.  Riddle’s greatest asset – his Slytherin ancestry – might swing things in his favour, but might not, since that ancestry came from an otherwise disreputable family and his dad was a muggle.