If there is no shady business between Putin and Trump why is Trump so far up Putin's *ss?

Trump declares Democratic governments of the EU foes, insults allies, ruins trade partnerships and goes against his own government and own party, which has ruled that Russia interfered in elections, but has little bad to say about a dictator who poisons his enemies (yeah, sure, there is no proof) and keeps taking rights away from the populace.

I do not understand. Enlighten me.