Does running for President give a candidate immunity from investigation of wrong doing?

No,no not doesn't.

However the timing and phrasing of such an investigation along with who was asked and under what circumstances does have a stench of using the office and position for personal gain.

It's an old Soviet tactic called kompromat. You save the misdealings and mishandling of people for when it is advantageous to your own means and ends as a tool.  Yes Biden's son does seem to have some corruption in Ukraine, that should not be forgotten.  However it is also underhanded to use that as a form of political ammo and try and use it only to stymie your opposition. Bad sport on both sides here.

As far as I know, the Constitution was NOT written by William Barr.

He will soon find that out, unless he is tried and convicted by the LIARS in the Supreme Court.  

So, it depends on what guy you are talking to.  Does the Constitution as it STANDS, count?  Or do illegal lackeys that were appointed illegally by a bunch of frauds count?

You decide. I know this, more people agree with me than you.  This is STILL a Democracy, fractured as it is right now, and TRUMP is not going to last out this term.

HE IS TOAST.  

No one is immune from being investigated for wrongdoing.