na-adjective
Used to describe matters, procedures, or decisions related to administration or the executive branch of government. Often appears in formal or bureaucratic contexts.
その決定は行政的な手続きに基づいている。
The decision is based on administrative procedures.
行政
An agency with executive authority conducted the investigation.
政治的 means 'political', referring to politics or policy-making, whereas 行政的 focuses on the administrative or executive implementation side.
Formed from 行政 (administration) + the adjectival suffix 的 (like, -ive). The derivation is straightforward and modern.