The president and his cronies have repeatedly claimed in public that they have evidence of massive fraud. They have not even attempted to claim any of these in court, where these claims would have been immediately discovered as outright fabrications.

Also, Trump has sought to buy out election officials with 'gifts', has cajoled and petitioned various others to ask for votes to be thrown out or 'discovered', has tried to convince congressmen and senators to overturn the result of the vote, has cobtemplated invoking marshal law and redoing the election and so on.

In all of this he has been successful in conning a large number of people that the most important democratic institution, the vote, has been stolen from them by the federal government and several states. They were convinced enough that they tried attacking Congress to force it to overturn the results.

If these are not aspects of an attempted coup, I don't know how they should be interpreted.