Never terribly coherent, Trump’s monologues have become even more long-winded and rambling. Even if he is fine (or at least no worse than he always was), he will be the oldest person to take office (Biden was a year younger when he took office) and it is reasonable speculate that Trump might not be up to the presidency. Is a vote for Trump, really a vote for JD Vance?
The speculation is that Trump will be displaced by the 25th amendment. This has never been done before and enacting it is no small thing. The amendment would work fine if the president was in a coma, but short of that it effectively calls on the VP to organize a coup against the president.
The 25th amendment establishes a regency, a recognized caretaker for an ill king. Another possibility is a Vice President Vance emerging as an eminence grise, the secret power behind the throne.

A quick look at past cases of incapacitated presidents shows that these scenarios are difficult to pull off and that the VPs have avoided any appearance of usurpation.
Vice Presidents, Presidential Incapacity, and the Dread of Usurpation
The most notable instance of presidential incapacity was Woodrow Wilson, who suffered a massive stroke in October 1919. His wife, the White House physician, and the president’s personal secretary collaborated to hide the president’s condition from official Washington and manage essential official business. When a Congressional delegation insisted on seeing the president, he stirred himself sufficiently to assuage their concerns. Vice President Thomas Marshall, who had almost no relationship with Wilson, was kept away from the White House. He was informed of some aspects of the situation through intermediaries but recognizing the gravity of the situation and not wanting to appear a usurper, Marshall took no action. (Much of the historical info can be found the great Jules Witcover’s The American Vice Presidency: From Irrelevance to Power.)
Eisenhower suffered a heart attack in the fall of 1955 and a stroke two years later. While the president convalesced, Vice President Nixon, who was probably more engaged with the White House than any of his recent predecessors, chaired cabinet meetings. Nixon was very young (39 when nominated for the vice presidency) and never really a member of Eisenhower’s inner circle. The inner circle of older men (including several prominent business executives) led by White House chief of staff Sherman Adams and Secretary of State John Foster Dulles kept the administration going. Nixon was credited for managing this difficult situation well, providing continuity without even the appearance of usurpation.
Nixon, in the throes of the Watergate scandal (and perhaps before) was not always coherent or measured in his exercise of power. There are also reports, particularly during the Watergate scandal, that he was using alcohol and pills. He also suffered from a painful bout of phlebitis and may have been self-medicating. Nixon’s closest associates had learned when to ignore presidential orders, as Nixon was famous for ranting when stressed. Kissinger stated that Watergate happened because the wrong people were in the room when Nixon was spouting off—although Kissinger himself followed unwise instructions at times. Agnew of course was nowhere close to any of this. When Agnew was replaced by Ford, the new vice president, as the depths of the political crisis became clear, distanced himself from the White House and remained mum as Congress investigated and began to prepare to impeach.
Reagan went through periods in which he was “out of it” (I believe that’s the medical term.) For a year or so after he was shot in 1981 Reagan wasn’t terribly focused. Later in his second term he was allegedly suffering from cognitive decline (in his post-presidency he was diagnosed with Alzheimer’s disease.) When Reagan had a strong chief of staff (James Baker in the first term and Howard Baker in his second), things went pretty well. The staff kept the wheels turning. Further, Reagan always had a hands-off management style in which he set broad direction and expected his staff to implement it. As an actor, Reagan would “hit the mark” in public appearances. When Reagan’s chief of staff wasn’t strong, things went off the rails and you got potential presidency ending scandals like Iran-Contra. Throughout all of this, Vice President Bush tread carefully. When Reagan was shot, Bush worked hard to ensure that there was absolutely no appearance of usurpation. The Secret Service urged him to land on the South Lawn of the White House when he returned to DC after the assassination attempt. Bush refused, insisting only the president lands at the South Lawn. When the vice president went to see the president in the hospital, he brought a folder marked “Top Secret” and made sure the press saw it, to give the impression Reagan was engaged.
Two other cases are worth mentioning, although the president was not incapacitated. When Clinton was impeached and tried, Gore was completely loyal. He had been selected in part because his associates assured Clinton that Gore would never stab him in the back, and this proved true.
No one thought George W. Bush was suffering from cognitive decline (although many doubted his brains from the beginning.) But Vice President Cheney, acquired a reputation as eminence grise, or Darth Vader. Cheney was certainly a capable inside player, but the idea that he was secretly running the country is a bit overstated. Cheney saw his role as enabling the president, taking care of things so the president didn’t have to. As Bush’s confidence grew (and the cost of Cheney’s policy preferences became apparent), the vice president’s role diminished. At the same time, Cheney’s increasing notoriety made him a lightning rod for criticism.
The final case might be that of Biden, although I am skeptical that he is truly cognitively impaired. He had a lousy debate performance, but shortly afterwards negotiated a complex multilateral hostage exchange. The GOP has argued that Harris has been secretly running the country, but this seems unlikely.
Implications for a Vance Shadow Presidency
The theme that continues to appear in this brief overview is that VPs have rightly avoided the appearance of being a usurper. VPs are akin to crown princes, and however much they may lust for the throne, they cannot measure the drapes.
But could Vance become a de-facto president? Trump has accumulated a cadre of wonks and operatives who could better staff the administration than in his first term. (By better, I mean carry out his agenda effectively—this analysis is agnostic about the possible outcomes of the policies.) A Reagan-like scenario in which Trump sets broad themes and his staff manages the details seems plausible. An adroit Vance could be part of the quartet or troika or whatever that manages the day-to-day in the Trump White House. Vance would need to take great care to not appear to be overstepping. This will be a challenge. As the administration fails to follow through on promises (pretty much every administration does) MAGA pundits will call for the administration to let Trump be Trump or accuse Vance of betraying the agenda and well… usurping power.
There is a complication to this scenario however, Trump is not Reagan. Back in 2016, I described Trump as the false Reagan. But I think he is more like Nixon. Reagan was personally mild and pleasant, as an actor he didn’t like to make trouble on the set. He was also famous for rising to the occasion in public appearances. Trump will be more of a mad king, unmanageable in public and prone to outbursts. Like Nixon, he may have a loyal cadre who will protect him from himself. But there are Trumpists who will rush to do anything the president asks and Trump can reach them, and his legions of devotees, directly via social media, issuing directives and guidance with no filter.
Vance has talent as a Trump explainer. But the scenario in which Trump is a mad king, with Vance as the power behind the throne in a court with literally millions of hangers-on would bring unimaginable chaos to Pennsylvania Avenue, and the nation.
Interesting!