In my experience, the “audits” are all automated anymore. The IRS will cross reference data you enter from a 1099 with data submitted by banks and investment companies. A college 529 seems to be a magnet for netting letters from the IRS. Their audits seem to always flag the gains as taxable even when the investments are in a 529. Suppose it could have been the way it was being reported by the investment firm.
So yes, I could easily see Trump getting audited pretty much year round every year.
I believe this is correct, as well. Their computers are programmed to look for certain things that have been abused in the past. For instance, if your medical deductions exceed a certain threshold, your return will be flagged. I don't know what point an agent actually reviews the flag, if at all.
I would expect Trump's individual return to be really complex, given all his different business ventures. It's not unreasonable for it to trigger an automated screening every year -- the question is how often would the IRS actually initiate an audit? If it's a different thing each year, he could easily be audited every year.