Agents are checking documentary evidence regarding Trump's income and expenses and determining whether he paid sufficient taxes and whether his statements to the IRS were accurate. The result could be no change, or a civil fine, or in certain events, criminal prosecution. It is most definitely an investigation. Focus on what is important, not on the word "investigation".
“Agents are checking documentary evidence regarding Trump’s income and expenses and determining whether he paid sufficient taxes and whether his statements to the IRS were accurate.”
That is correct. Do you think Trump filed his own taxes? I think his return is a foot thick. It took many accountants many hours to roll that out, and Obama has a grudge against him.
The vast difference between Hillary and Trump is that Hillary knowingly, with malice aforethought, ordered, by her authority as Secretary of State, the circumvention of stated laws of security of the the nation and placed the nation at risk. That is just referring to the emails.
If you really cannot see the difference, then there is no point in pursuing this discussion.