Politicians used the press conference as an opportunity to vent their spleen on reporters.
(often + on)
vent (one's) spleen
To voice one's anger. Mom's been venting her spleen to me for an hour already. Apparently, Aunt Marie has wronged her yet again.
vent one's spleen
Fig. to get rid of one's feelings of anger caused by someone or something by attacking someone or something else. Jack vented his spleen at his wife whenever things went badly at work.Peter vented his spleen on his car by kicking it when it broke down.