I have a question about their safety. There is always people that bring up worries over some of the public sector pension schemes in the US and how it will aff

I have a question about their safety. There is always people that bring up worries over some of the public sector pension schemes in the US and how it will affect a municipality. One example, IIRC, is in Chicago. Another typically revolves around policeman/fireman pensions in other cities and the cities not being able to actually pay them. Is this a fault or mismanagement or the pension structure not working or both? And if the cities have to guarantee the pensions, what does that mean for taxpayers in those cities?