No major party ever has nominated someone without any experience in government office. All without any elective experience, or appointive experience to the executive or judicial branches at the state or federal level, served in high-ranking military positions. Even the least politically-experienced nominee, newspaper publisher Horace Greeley, served a few months in Congress almost a quarter of a century before receiving his nomination by the Democrats.
Trump’s success largely comes from frustration that many Republican voters have from Democrats in office who, with increasing success and brazenness, have transformed the country away from the fundamental principles behind its founding, and with Republicans officeholders seemingly unwilling to stand athwart of this sellout. Seen foremost by many as a successful businessman whose blunt style and win-at-all-costs attitude, reinforced by his celebrity status, this ultimate outsider status gave him cachet as someone so alien to current officeholders who themselves seem so alienated from the many that he has the greatest capacity to disrupt a system increasingly seen as detached from the people, if not corrupt.