To seriously answer your question..........
The Dems hate him because he's a serious threat to their money laundering our tax dollars into thier private overseas accounts.
Trump is a threat to their Communism and Marxism propaganda to the stupid and gullible, in order to destroy this country so they can literally take over as Tyrannical Dictators.
Trump is a threat to their personal agendas to sell out the USA to China and/or Russia.
Trump is a threat to all the major corporations in the USA that have sent all American jobs overseas or to Mexico, and left Amercans homeless and to starve.
Trump is a threat, as HE wants this country SAFE AND SECURE FROM OUR ENEMIES AND ILLEGALS WHO WOULD MURDER US IN OUR SLEEP AND SELL OUR KIDS DRUGS!
Trump is simply a THREAT to THEIR way of corrupt and criminal lifestyles of murderous debauchery, treachery, treason, and easy money.