Donald Trump spent much of 2016 questioning his opponent's stamina to be president of the United States.
But it is now Trump's own fitness that is being scrutinised by friends and foes alike.
After Trump spent recent weeks creating a level of chaos unseen around the White House since Richard Nixon's resignation in 1974, Capitol Hill politicians and media outlets are quietly questioning whether Trump is fit for the highest office in the land.
That the commander in chief slurred his way through the end of a speech on Jerusalem on Wednesday was just the latest in a string of unsettling incidents, reports The Washington Post.
Many who move through his orbit believe Trump is not well. That is a verdict that was reached long ago by many of the president's own staff. More than a few politicians and reporters across Washington have shared similar fears.
Senator Bob Corker openly questioned Trump's competence and suggested that administration officials are doing little more than running "an adult day care centre."
The chairman of the Senate Foreign Relations Committee also expressed fear that the president's erratic behavior is putting the United States "on the path to World War III."
The secretary of state reportedly called the president a "moron."
The national security adviser allegedly said Trump has the mind of a "kindergartner."
John McCain's 2008 campaign manager Steve Schmidt said on Thursday that "the question of his fitness, of his stability is in the air."
Unfortunately, Schmidt is right. With the pace of headlines detailing Trump's erratic behaviour quickening, so, too, are questions about his well being.
White House insiders tell Vanity Fair that Trump is "unravelling" mentally.
One of the president's regular early-morning reads, the New York Daily News, editorialised last week that "the President of the United States is profoundly unstable. He is mad. He is, by any honest layman's definition, mentally unwell and viciously lashing out."
The New York Times' Maggie Haberman, who, along with The Post's Robert Costa, has the best working relationship with this White House, described Trump's recent behaviour as "unmoored."
She told CNN, "Something is unleashed with him lately. I don't know what is causing it. I don't know how to describe it." Haberman's long history covering Trump makes her searing observations all the more troubling.
The president has spent the past few weeks insulting the United States' closest allies, retweeting anti-Muslim videos from far-right British activists, spitting out racist slurs at a ceremony honouring Native American veterans, privately embracing conspiracy theories related to his Access Hollywood tape and Barack Obama's birthplace, slandering CNN International, and, yes, pushing a bizarre conspiracy theory in my direction.
Any Fortune 500 company would have fired a chief executive exhibiting similarly erratic behaviour long ago. Unfortunately, the Washington leaders most strategically positioned to limit the damage seem to be frozen by fear.
The president's meltdown could not come at a more perilous time. For months now, national security insiders have been fretting about the possibility of war on the Korean Peninsula.
But administration sources admit their greatest fear is their own commander in chief's instability.
That should surprise few Americans. In August 2016, Mika Brzezinski and I reported on Morning Joe that then-candidate Trump horrified foreign policy briefers by how flippantly he mentioned the option of using nuclear weapons on countries such as North Korea and Iran.
During a 2016 interview with Chris Matthews, Trump even refused to rule out the use of such weapons in Europe and the Middle East.
Mika grimly warned viewers that a Trump presidency could lead to nuclear war. She implored Republican leaders to pull their endorsement of the troubled candidate in the best interest of their party and country.
Many close to the candidate expressed concerns on background about Trump's fitness for office.
That is a conclusion Mika and I reached two years ago this week when Trump unveiled his Muslim ban proposal. Two years later, Trump has dragged America's values and reputation to their lowest point in years.
If Republicans don't find their bearings soon, it may be America's safety and security that are next to go.
• Joe Scarborough, a former Republican congressman from Florida, hosts the MSNBC show Morning Joe.