(CNN) In the wake of three days of erratic behavior and amid the controversy caused by a book suggesting he is forgetful and dismissed by many who work for him, questions of President Donald Trump's mental competence are everywhere.

At Thursday's press briefing, White House press secretary Sarah Sanders called the idea that Trump was mentally unfit for the job "disgraceful and laughable." She added: "If he was unfit, he probably wouldn't be sitting there, wouldn't have defeated the most qualified group of candidates the Republican Party has ever seen."

While it's far from a determinative explanation from Sanders, she does have a point. And the point is this: Trump is who he has always been.

Think about the sorts of behaviors that Trump's critics point to as examples of his lack of mental competence or deteriorating mental state:

There are others, of course. But these, I think, broadly cover the competence critique made against Trump.

Now, go back over that list. And ask yourself whether any of those behaviors are new since Trump has been elected president.

While you're doing that, let me remind you that Trump did the following things as either a candidate or private citizen:

Impersonated a young publicist within the Trump Organization to leak flattering details about his own personal life to the New York tabloids.

Spent several years pursuing the totally debunked idea that President Barack Obama wasn't born in the United States

Made a series of lewd comments about women caught on tape by "Access Hollywood" (and then argued the tape might be a fake)

Insisted that 3-5 million votes were cast illegally in the 2016 election

Suggested Ted Cruz's father might have been involved in the assassination of John Kennedy

Those are the ones I came up with off the top of my head. There are scores of others examples just like them.

There is a clear pattern of behavior there that long predates Trump's time in the White House or even his decision to run for president. Trump is today who he has been the entirety of his adult life.

That is a person that many Americans find to be loathsome. Or incompetent. Or mentally unwell.

He is also the person who 62,984,825 people, or 46.09% of US voters in 2016, supported -- and those people happened to live in just the right states for Trump to win the electoral college even while losing the popular vote by a historic margin.

Given his prominence in the culture and the incredibly high profile of the 2016 presidential race, it's very tough for me to believe that the people who voted for Trump did so without knowing who he really was. The Trump on the campaign trail -- full of bravado, fiercely unapologetic, dramatic, obsessed with victimization -- was the Trump of the wheeling-and-dealing 1980s. It was the Trump of the reality TV show years. And it is the Trump of the White House.

The obvious pushback to this argument is that simply because Trump's behavior isn't inconsistent with who he has been his entire life doesn't mean that he is mentally well enough to hold the office of the presidency.

Fair enough. I am not a psychologist or a psychiatrist, so diagnosing what, if anything, has long been wrong with Trump mentally (and if that impedes his ability to do the job) is well beyond my skill set.

But what seems clear -- at least to me -- is that the case for some sort of mental deterioration from Trump since he has been in office simply isn't there.

Is it possible Trump has sunk more into his ways and habits (and insecurities) as he continues to age? Sure -- since lots and lots of people do exactly that as they get older.