I don't see how you could claim - off the cuff - that the Democratic candidates are more intelligent and competent than Trump. Can you elaborate?
Regarding "competence" - I think it's important to clarify what we are judging competency *in*. DJT is a showman and realty TV personality who inherited his father's real estate business and hundreds of millions of dollars. Points can be made about whether he has been a 'successful' businessman or not, but I think a fair reading shows that he was a successful (e.g. competent) realty TV star.
However, when evaluating him
as a president I think his record shows an incredible amount of incompetence
in government. He and his team came in woefully unprepared, and for the past two+ years he's made one unforced error after another. Anyone with a modicum of governmental experience knows that you should first have the support of your own party before nominating someone or proposing some piece of legislation. There's even a position in the legislature designed to tally such support (the majority/minority "whip"). Yet Trump has needlessly spent political capital nominating people who his own party wouldn't support (e.g. Ronny Jackson), or who hadn't been properly vetted (e.g. David Clarke, Monica Crowley), or who was so inexperienced for the job they were nominated to that they've been un-effective (oh so many... but Kushner tops the list, but also Carson and McMahon and DeVos and...). Some of his most important cabinet members he didn't even seem to like or care to work with (Tillerson for his entire tenure, Sessions for 90% of his)
He's also has a poor track record proposing policy that almost everyone paying attention was certain would get stopped by the courts (various immigration EOs come to mind) or proposing someone that only drew an enormous partisan fight (Kavanaugh). Behind closed doors I'm sure most in teh GOP wished Trump had nominated a staunch conservative with far less baggage - and the list of potential candidates is very long there.
Then there's the policies that he
hasn't done. Rather than pushing through a large infrastructure bill when the GOP controlled all branches of government and he could have easily gotten several dozen Dems to join (everyone likes to bring $$ to their home district) he went deep into a bunch nof cultural fights no one wanted (e.g. "very fine people on both sides" and attacking NFL players). He (again) forced a vote on the ACA without any viable alternative and when he had a razor-thin margin for repeal... and ultimately lost. He repealed NAFTA and now is struggling to get its replacement approved by his own party (which is pretty darn similar to the trade agreement he ripped up). He withdrew from the Iran deal but hasn't been able to work with either our allies OR Iran on the very issues we supposedly withdrew for.
Finally, DJT arguably cost his party the house, as extreme displeasure of his presidency drove substantial turnout in a non-presidential year.
In all of these cases a seasoned political advisor would have pointed out the obvious: These actions are losers, and the same goals could be achieved with less baggage.