I blame the creators of The Apprentice most of all. He was already fading from the media spotlight when they resurrected him for the masses. It debuted shortly before he hosted SNL.
Speaking purely anecdotally, I think
The Apprentice was pretty much the way most Americans defined Trump prior to 2015 or so. Even during his non-campaign in 2011, which is around the time he seemed to discover Tea Party-style Faux-Populism as a way to garner free publicity, he was always "Businessman/CEO and Reality TV Show Host Donald Trump" before he was anything else. The idea that he even
could be a serious political candidate didn't show up anywhere until c. 2015.
At that point, I think he basically won his first election by sheer inertia. Historically, American patterns of voting have changed significantly due to seismic political shifts like the War of 1812, the rise of Jacksonian Democracy, and the Civil War, but the Post-WWII cultural environment has generally being a swinging pendulum favoring that each party hold at most two terms in the chief executive office, with the rare exception of George H.W. Bush reflecting an unusually strong and lasting shift to the Right under the Reagan Administration. President Obama was mostly mediocre, not terrible but not great, and had basically no chance of keeping the seat warm for a Democratic successor during his last term in the Oval Office. The problem for the GOP establishment, which was most likely to win in 2016 no matter who they ran, was that nobody actually
liked any of their mainstream candidates. Jeb Bush and Newt Gingrich were not drawing in crowds at primaries. Trump, on the other hand, suddenly had an advantage in being the
Apprentice guy. He was a brilliant showman, probably not actually expecting to win at the outset, but aware that he could both use a failed campaign as a money maker in its own right and establish himself as a force in partisan Republican politics, encouraging candidates to support his business and personal interests in exchange for endorsement. Using his role on the show for initial clout, he saw an opportunity to move beyond that, and he took it.
Building a cult of personality as a kind of viral marketing is actually pretty ingenious. Not in a way that qualifies you to be head of state of a nuclear-armed global Hyperpower, but still pretty smart. Once he won the primary, he didn't have to win the general election. Broader political forces all but guaranteed he would. All he had to do was to stay inoffensive enough to
not actively lose, and with the Democratic candidate being a bland 1990s-era Neoliberal whose fame had peaked almost 20 years ago and whose sole unique quality was having a vagina rather than a penis, that was as easy as not getting a swastika tattoo and/or threatening to start a global thermonuclear holocaust. The fact that his name recognition came primarily from an already well-past-its-prime cable TV show, and that his actual business ventures ranged from standard-issue inherited investments to bankrupt failures, no longer mattered. He just had to be well-known enough to get his supporters to the polls, and to avoid doing anything so terrible that his opponents would get out in large numbers.
After winning a presidential election, you're always going to be "Former President", whatever your initial claim to fame. Anyone who thinks he's actually more of a businessman/politician than a celebrity is just delusional, though. Even pre-
Apprentice, and post-election, he's still mostly known for what are mostly deliberate marketing stunts and engineered controversies. You can see how differently he handles the backlash from obvious engagement-driving "controversies" (Gulf of America, 'shithole countries', the Kim Jong-Un Twitter exchange, 2020 election conspiracies, etc.) and actual, potentially-damaging controversies. Things like the consequences of the
Dobbs decision, Hurricane Maria, or the US withdrawal from Kurdish-majority regions in Iraq get deliberately buried or distanced from him as far as possible, even when his role in them is undeniably substantial. He's great at garnering publicity, and unbelievably shitty at actually making decisions rather than following plans drawn up by others.