Final answer:
Federal judges must maintain 'good Behavior' as required by Article III and remain free from undue political influence thanks to their life tenure.
Step-by-step explanation:
To maintain their eligibility, federal judges must adhere to two main principles established by the U.S. Constitution: uphold 'good Behavior' as mandated by Article III, and remain free of undue political influence due to their life tenure. These principles ensure that judges can operate with judicial independence, making decisions based on the law rather than external pressures. Although not constitutionally required, it is also a de facto standard that federal judges be well-educated in the law, typically having graduated from law school and often having experience as attorneys or at various levels within the judiciary system.