You're missing one important thing here. These spendings that Serenata's robot tweets are literally reimbursements that congresspeople receive from the federal

You're missing one important thing here. These spendings that Serenata's robot tweets are literally reimbursements that congresspeople receive from the federal government for spendings needed while "on duty". They aren't paid using their salaries. If that was the case, there would be no problem (legally speaking).