Because the cloud of an investigation hurts a candidate, even if its a witch hunt.But if the Bidens did nothing illegal, what does it matter if they're investigated?That's manufactured bullshit which only a retard buys.It is if it is a way to launder payments to the Biden's to buy influence with VP Biden and the state department.That is not illegal.
If Trump did nothing illegal why was Trump such a snowflake whining about the investigation?
This works, as example: a week before 2016 vote, Comey announced re-opening of Hillary email issue, which helped Trump and hurt Hillary.
Whining about the investigation doesnt help either.
Which of course exactly explains why Trump wanted Ukraine to make a public announcement that they were investigating the Biden's.
The cloud of investigation.