GAO dug into just four trips over the span of a month at the beginning of Trump's term, Feb 3-Mar 5, 2017.
DOD/DHS costs ran to nearly $13.6 million.
Another $3 mil was spent on transportation, lodging, meals, incidental expenses for traveling govt personnel.
The Secret Service spent nearly $400k to protect Donald Trump, Jr. and Eric Trump on three trips, while they traveled to Uruguay, the Dominican Republic and the UAE in early 2017.
GAO says most Secret Service agents stayed at nearby hotels.