&quot;Designated Survivor&quot; scenario: What if a President is sworn in and someone earlier in succession resurfaces?
<p>If something like what's depicted in "Designated Survivor" (TV-show) happened – POTUS, VPOTUS, Speaker, &amp;c, were all (believed to be) dead – and the "designated survivor" had become <strong>acting President</strong> and then sworn in as President:</p>

<p>What would then happened if someone further-up the line of succession were found to be alive?  Would the new President then be automatically removed from office? 
Or would he remain President even if it turns out he was sworn in by error? 
 Would he be obliged to step down?  Could he refuse?</p>

<p>If he didn't step down, would the one higher up in the succession have a claim on the office?  Could he too be sworn in, and become sort of an "anti-President" (like how there were two Popes – the Pope and an "anti-Pope")?</p>

<p>Would it matter who resurfaced?  For example, is the answer different if it was the Vice President who was later found alive, or some other elected official (e.g., the House Speaker) instead of "just" another (but higher-ranking) appointee?</p>

<p>And what if the President himself was found to be alive days later (and still able to perform his functions)?  Would that compel the new acting President to step down?</p>

<p>Once a person is sworn in as POTUS, there are only two legal mechanisms for involuntary removal of that person from the office:</p>

<p><a href="https://www.law.cornell.edu/constitution/articleii" rel="nofollow noreferrer">Article II Section 4 of the U.S. Constitution</a> provides only that:</p>

<blockquote>
  <p>The President ... shall be removed from office on impeachment for, and
  conviction of, treason, bribery, or other high crimes and
  misdemeanors.</p>
</blockquote>

<p><a href="https://www.law.cornell.edu/constitution/amendmentxxv" rel="nofollow noreferrer">The 25th Amendment</a> was passed to establish clear procedures of official succession.  Its Section 4 also provides an elaborate mechanism whereby "the Vice President and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide" can precipitate a process that would allow Congress, within 21 days, to transfer the office to the Vice President.</p>

<p>Otherwise, there is no contemplation in the law of a "backsies" mechanism for removing a person from the office because "it should have gone to someone else."</p>

<p>(The idea that a person who <em>was</em> in the designated line of succession, but in the wrong order, was sworn into office does not seem nearly as problematic as other events that have happened in real history.  For example, in the 2000 Presidential Election it was conceivable – and some people probably maintain in fact – that the "loser" of the election would be sworn into office.  <a href="https://en.wikipedia.org/wiki/Bush_v._Gore" rel="nofollow noreferrer">The U.S. Supreme Court settled the legal questions</a> before the inauguration.  However, the realization at the time was that any legal challenges or decisions after that date would be moot, because "election error" is not a cause to remove a sitting U.S. President.)</p>

<p>The question of a previous President reappearing, and his successor refusing to cede the office, takes us to the height of speculation.  In this case I would merely note that I can find no law pertaining to <a href="https://www.gsa.gov/governmentwide-initiatives/presidential-transition/legislative-overview/presidential-transition-act-of-1963" rel="nofollow noreferrer">Presidential Transition</a> in which an outgoing President is "stripped of authority" or "removed from office."  Rather, the acting POTUS is effectively <em>the most recent person sworn to the office, and not removed from it</em>.</p>

<p>Not sure what you mean by "had become acting President and then sworn in as President". Only the Vice President can actually become President. Everyone else on the line of succession can only act as President, not actually become President, according to Article II, Section 1, Clause 6 of the Constitution (and presumably if they were sworn in, it would be as Acting President).</p>

<p>If the Vice President were the designated survivor, and the President's fate is unknown, rather than assume that the President is dead, he (in combination with a majority of the Cabinet) could simply declare the President to be unable to discharge the duties of his office according to the 25th Amendment, section 4. In that case what happens is clear; the Vice President is rightfully Acting President until the President transmits that he is able to discharge the duties of his office again (and possibly have to wait 4 days after that in case the VP and Cabinet wish to counter that declaration). Even if the President reappears, the powers of the Presidency would still rightfully belong to the VP until the President makes this declaration.</p>

<p>If the President and Vice President's fates are both unknown, then it's tricky. Article II, Section 1, Clause 6 of the Constitution provides that when the President and Vice President are both unable to discharge the duties of their offices, Congress provides by law (the Presidential Succession Act) who acts as President. The problem is that unlike for the President, there is no constitutional provision specifying a way to declare the Vice President unable to discharge his duties. So unless the Vice President is known to be dead or the Vice Presidency is vacant, there will be questions about whether someone later in the line of succession can rightfully act as President or not. Assuming that this person can rightfully act as President due to disability of the President and Vice President, Article II, Section 1, Clause 6 clearly states that they act only until the disability is removed (of the President or Vice President). So if the Vice President or President shows up, presumably they take over, though again in the case of the Vice President, there is no constitutional provision specify how to declare that a Vice President is able to discharge the power of his office again.</p>

<p>This problem with lack of a provision to declare that the person is unable to discharge the powers of their office, or that they can discharge the powers of their office again, also exists for everyone further in the line of succession (provided by the Presidential Succession Act), so let's ignore it for now.</p>

<p>If the President pro tempore of the Senate is acting as President, the Speaker of the House becoming able to discharge the powers again doesn't bump the President pro tempore, because section (c)(2) of the Presidential Succession Act specifies that the Speaker or President pro tempore continues to act as President unless the President or Vice President's disability is removed.</p>

<p>If a Cabinet member is acting as President, section (d)(2) of the Presidential Succession Act specifies that they continue to act as President unless someone higher on the list can act, but not counting if a higher Cabinet member's disability is removed. This means that if the Speaker of the House or President pro tempore of the Senate can discharge the powers of their office again, they will bump the Cabinet member currently acting as President, but if another Cabinet member higher on the list can discharge the powers of their office again, they will <em>not</em> bump the Cabinet member currently acting as President. Some scholars believe that the "bumping" provision may be unconstitutional as the Article II, Section 1, Clause 6 of the Constitution says Congress provides by law the single officer who will act as President, and that this officer "shall act accordingly, until the Disability be removed, or a President shall be elected", with no allowance for passing the powers between different officers prior to the removal of disability of the President or Vice President.</p>

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