> A small town mayor has none of the power a member of congress would.
Assuming the mayor is in an executive mayor system (not a council-manager) system, they often have far more practical power than a member of Congress over any issue, but their power is over smaller issues. Even in a council-manager system, the mayor (who is a primus inter pares council member) is more likely than member of Congress to have decisive power over any issue within their ambit.
(Also, being a small town mayor, or similar local officer, is not an uncommon way to build the infrastructure for becoming, say a state legislator. And that's a way to build the infrastructure for Congress, and that for Senate/Governorship, and that for the Presidency.)
We are discussing a conspiracy that requires the cooporation of hundreds of worldwide governments. The process to gain the power of your "congress" is fairly insignificant within this discussion. There are many governments with varying paths to power.
A small town mayor has none of the power a member of congress would.
In democracy the larger the seat, the larger the infrastructure required to get there.
The funding of this infrastructure brings the necessity of corruption.