Please explain to me why this Trump/Ukraine thing is a big deal

It seems to me that President Trump was trying to remedy the wrong of Biden using his official position and the threat of withholding aid money to Ukraine to protect his son from an investigation by the Ukranian prosecutor. Sherrerd’s post seems to me slanted to ignore Hunter (and Joe) Biden’s wrongdoing. At least, that’s how it seems to me from a first pass of what’s been released so far.