The way that Trump is undermining democracy is far more insidious than anything dictators like Hitler used to seize power. Trump has no ambitions to become an authoritarian dictator and I personally find it ridiculous that people make comparisons between him and Hitler, for example. However his narcissism and egoism has led him to issue personal insults against others and more importantly lead attacks on any news that is unfavourable to him and the free press. Unable to stand the criticism he receives, he has harnessed the extreme levels of support voters have given to him to attack some of the key tenets of liberal democracy and in doing so sown ever greater partisan division. Although these issues of partisanship existed before Trump's rise to power, he has exacerbated them and as the Leader of the Free World, his use of these tactics has greater legitimised them. Even if Trump goes in 2020, his impact will be felt for long afterwards.
Yes the economy is booming, but Obama deserves the credit for rescuing America from the greatest economic crisis since the Great Depression and setting the country on its current economic path. I personally do not think his trade spat with China is a bad thing with China's aggressive and ever-growing trade power a genuine concern for America. However what Trump needs is allies and his bullying of his strongest allies such as Canada and the EU regarding trade is ridiculous and at a time when liberal democracy is under ever greater threat from Russia, China and others, his actions are incredibly ludicrous. You cannot and should not run a country like a business.
His supposed successes with North Korea are nonexistent as well. North Korea have not disbanded their nuclear weapons and their summit together was rather farcical, achieving nothing, but giving Kim Jong-Un time under the global spotlight. Instead it is South Korea who's new, less hardline president, Moon Jae-In who should be getting the credit for actually deescalating the tension.
As much as Trump is fulfilling his campaign promises, to me it appears Trump has no intention of fulfilling the role as President fully. It is only an ego boost for him and he detests the long hours and hard work actually involved with the boring day-to-day issues, instead enjoying big rallies and press events far more. As a result, his administration is being woefully run with there still being unfilled positions and scandals almost weekly such as Pruitt's misuse of public funds and blatant links with coal and gas despite being head of the EPA. Moreoever, I don't think it is truly correct to say that he is fulfilling all of his campaign promises. He told supporters that he would "drain the swamp" and acted as an anti-disestablishment figure. His tax cuts for the richest, placement of his own family, wealthy Goldman Sachs bankers and people with links to coal, oil and gas in positions of power show that he is in actuality perpetuating the power of the swamp at the expense of most of his base.