Does it violate the Appointments Clause for a Circuit Judge to be appointed to sit continuously as a District Judge by another Circuit Judge?

1. Under Article II, Section 2 of the Constitution, principal federal officers, including United States District and Circuit Judges, must be nominated by the President and confirmed by the Senate to their office. Does it violate this Appointments Clause for one Circuit Judge to appoint a fellow Circuit Judge to sit continuously for years as a District Judge? 2. Section 291(b) of Title 28 permits a Chief Circuit Judge to “temporarily” designate a fellow Circuit Judge “to hold a district court” when it is “in the public interest.” Does it violate this statute for a Chief Judge to appoint a fellow Circuit Judge to sit continuously for years as a District Judge? 3. When a defendant on federal supervised release faces a n alleged violation subjecting him to additional mandatory prison time and an increase in the maximum punishment beyond that authorized by his original conviction alone, d o the Fifth and Sixth Amendments require the violation to be tried before a jury and proven by more than a preponderance of the evidence?