Question

What protects federal judges from political pressure to make a certain ruling?

Answer 1

I believe the answer is: B. Federal judges serve for life, and so do not need to worry about conforming to the wishes of others to be reelected.

If the federal judges is appointed everytime the president is changed, the elected federal changes would most likely a person who are picked to serve the best interest of the president in command. By making them serve for life, this situation become less likely.

Answer 2

Unlike State court judges, which in many States are subject to election, Federal judges are nominated by the President and confirmed by the Senate, and only then are appointed to the Federal bench. Federal judges remain in office as long as they want to. Federal judges are only subject to discipline for misconduct through impeachment in and by the U.S. House of Representatives and removal from office upon trial and conviction in and by the U.S. Senate. 

Obviously, then, any ruling that would arise from and comprise actionable misconduct would be avoided by federal judges. Actionable misconduct does not necessarily include rulings that are alleged to be politically motivated. The U.S. Constitution defines actionable misconduct as "high crimes and misdemeanors", and there are statutes, rules, and common law which define these.