There’s is corruption you would find many evidences in form of court verdicts international reports etc. Moreover a sane person through observations can tell if a politician is doing his work in the best manner or not and you can share , post your review with others. But when you accuse a specific person of doing a specific evil act you should have evidence to back your claim. In politics it’s usual for politicians to accuse each other without evidence and the party followers repeat those accusation without evidence ,it’s prohibited as in surah al a’raaf God mentions البغي (i.e transgression) a prohibited thing. When you accuse someone without proof you’re transgressing against their respect, Honor etc.