In my opinion, the main reason is the lack of political experience and knowledge. Being a great showman and businessman is not a guarantee of success in politics. It is possible to get the presidency with the help of various technologies and circumstances, but it is problematic to stay in power.
Since Trump has never been involved in politics, has never been in an elected office, then, accordingly, he did not have a team. Therefore, he had constant personnel scandals. There were random people among the appointees who annoyed the establishment of the Republican Party, in which he is still considered an alien element.
After the triumphant elections, he had to immediately begin to change the archaic electoral system, according to which the fate of the future head of state is in the hands not of ordinary Americans, but of the electoral college, which is completely controlled by the US elites. However, he did not.
The current presidential race was not organized in favor of Trump. The liberal media demonized him and created an unequal atmosphere in which the elections were held. And the president himself added fuel to the fire.
Any criticism in his address was immediately called "fake news".
Election rules under the US Constitution are not determined at the federal level, but at the state level. And here neither Trump nor his aides changed anything, did not make any necessary adjustments.
The Democrats masterfully dragged the president into impeachment proceedings. It took away a lot of time and energy from him in the fight against dismissal and constantly distracted him from the elections.
Trump has filed numerous lawsuits in courts, all the way to the Supreme Court. And he could not legally prove the facts of massive falsifications that significantly influenced the outcome of the elections. The loss had to be admitted. He didn't.
But the president decided to enlist the support of the street. He called his supporters to a rally in Washington. At least 100,000 Americans arrived in parliament, demanding re-elections. Trump publicly called on Pence, under crowd pressure, to refuse to accept the results of elections in 5 states and to announce a new vote there.
Pence flatly refused. And the uncontrolled part of the radical Trumpists took the US House of Representatives. Trump had no Plan B. He got scared and turned to law enforcement agencies to clear the Capitol from the protesters.
What's next? On Monday, Democrats will try to begin the process of impeachment of Trump for his incitement to state insurrection.
The Democrats will most likely try to finish off the president.
The lower house of the US parliament will vote for his removal. There, the majority belongs to the representatives of the Democratic Party. However, the final decision is with the Senate. And the Senate is not in session next week. In order to gather senators, you need their personal 100% consent. And this is unrealistic. Therefore, if impeachment happens, it will only be after January 20, when Trump will lose his post.
After the by-election to the Senate in the state of Georgia, where the Democrats won, it will not be a problem to make a decision that will ban Trump from running for any public office and participating in the presidential elections.
But Trump has little opportunity to avoid public embarrassment. It is to voluntarily resign in the coming days at will. Then Vice President Pence will be acting president until Biden's inauguration and can, if he wishes, pardon Trump. Under such conditions, Trump will not be prosecuted at the federal level.
But will Pence do it? It is very doubtful, since Trump publicly quarreled with him and considers him a traitor.
If we assume that bridges will be built between Trump and Pence and a voluntary departure from power will still happen, then this will not apply to Trump's persecution due to violation of state laws. As you know, in particular, in the state of New York, the president is accused of financial violations. Here he can have very serious problems.
It is not long to wait for Biden to begin his term - with an attempt to sew a divided country or with finishing off Trump. Whatever it was, after January 6, the United States lost the moral right to teach other countries how to live and how to organize the functioning of its government.