Will Trump be remembered as one of the biggest mistakes America has ever made?

Only if he starts a war with Iran. Trump's policy is terrible, but it's hardly an aberration from the norm. The president before him fucked up the Libyan state and levied a specific tax against the poor, and the president before him killed 200,000 people for no reason and deregulated the banking industry. The only reason why Trump gets singled out as the big problem is because he's the only president who deliberately trolls his rivals and says ridiculous things.