The phrase "presidential oath" refers to a promise that someone takes when they become the President of a country. It is a formal commitment to faithfully carry out the duties of the presidency and to uphold the constitution. Full definition
Nor is «so help me God» part of the presidential oath of office. (christianitytoday.com)
(What is part of the presidential oath is a promise «that I will faithfully execute the office of president of the United States.» (christianitytoday.com)
President - elect swearing in the Presidential oath regarding workplace to protect, shield, as well as... silver dimes value (religion.blogs.cnn.com)