So theoretically if any one of the party in american system gets 2/3rd people of the same party and they all agree to one person and try to amend the constituti

So theoretically if any one of the party in american system gets 2/3rd people of the same party and they all agree to one person and try to amend the constitution itself to add whatever they want, can't they theoretically create a purest form of dictatorship (one which lasts forever instead of just 5 years) I mean given how much is already happening in America, I am just curious from a legal standpoint if there could be done something like that (forgetting the insane backlash but still), what could the president of america do to completely sieze the constitution ?