The Senate has to approve a cabinet member's hiring, but not their firing. If the existing head of a cabinet is fired, acting heads are typically assigned based on a line of succession. In this hypothetical, let us assume that the top 3 candidates in line of succession are from the opposite party and the 4th person in line would represent the interest of the President.
If the Senate and the president are from opposing parties, is it possible for a president to circumvent the Senate confirmation process by selectively firing the top three people in line thereby making the fourth person the acting cabinet members? How long can the acting head act without being confirmed by the Senate?