Stop spending appropriated funds on travel for any reason. Every legitimate reason to conduct government business can be accomplished using video teleconferencing (VTC). If someone the POTUS needs to speak with does not have VTC capability, it can be provided by the United States for much less than would be expended by physical travel. By using VTC to conduct government business you would be maximizing time available to the POTUS by eliminating time required for travel and increase security to government employees by eliminating the need to place them in harms way in other countries.
Using VTCs instead of travel would also significantly reduce the funding required to support the office of the president.