President Nixon could have been convicted.
Presidents don’t have more (or less) immunity than their subordinates such as Hillary Clinton[Libya], General Eisenhower[French railway bombing], General Westmoreland[napalm], Colin Powell[testimony], J. Edgar Hoover[spying on MLK Jr.], James Comey, Eric Holder or Merrick Garland.
Presidents do enjoy a rebuttable presumption that their actions were legal.
“Presidents don’t have more (or less) immunity than their subordinates...”
You are conflating an elected president with appointees.
Judges have immunity. Congressmen have immunity while on the floor and Congress is in session.