Among grassroots Republicans and conservatives, it was Donald Trump's stands on immigration and trade that really resonated and set him apart from the other Republican candidates. The Flyover-Country base of the GOP has long been more populist on these issues than the more business-friendly Republican Establishment, and in Trump they found a spokesman. It deserves discussion that the candidate that gave voice to the concerns of working class Reds happens to be a billionaire from New York City, but that is for another time.
On foreign policy, Trump did an amazing thing that no one could have predicted before this election cycle started. Trump, the Republican nominee, ran as the less hawkish candidate on foreign policy. Whether this was primarily by design or by accident is not entirely clear, but it makes more sense within the total package of Trump's somewhat inchoate but identifiable political philosophy than many might believe. That Hillary Clinton deliberately embraced the more hawkish, internationalist position to take advantage of Trump's unique among Republicans foreign policy views seems clearer.
What role Trump's more restrained foreign policy played with his Flyover-Country base that enthusiastically embraced his populist appeal on immigration and trade is also not clear, although it didn't seem to hurt him for the most part. Trump's main detractors on foreign policy were movement conservative and neoconservative ideologues in the NeverTrump effort, who proved to not carry nearly as much sway with rank-and-file Republican voters as they thought they did.
Trump gave the foreign-policy element of the conservative coalition red meat on going after ISIS and opposition to the Iran deal, which is likely the cost of admission to seriously compete in a Republican primary, but he also managed some remarkable things that should not be overlooked in the aftermath of his victory. Trump very specifically condemned the invasion of Iraq. Whether he was on record in opposition to it prior to the invasion is a subject of some dispute, but he was clearly on record in opposition to the war fairly early on, long before many other war critics came around. He also specifically questioned the judgement of President George W. Bush and even claimed during the South Carolina primary debate that Bush lied the U.S. into the war, and this in a state that is very military friendly. Trump's Republican critics at the time were confident this supposed gaffe was going to doom Trump in the GOP primary but it did not. Trump cruised to an easy victory in South Carolina and beyond.
As a veteran of the intra-conservative foreign-policy debate, it is difficult to overstate the significance of this. Just a decade ago such views would have marginalized any Republican primary candidate who espoused them. Just ask Rep. Ron Paul, but they did not seem to seriously damage Trump.
To what degree Trump's supporters fully embraced his foreign-policy positions, were able to overlook them or didn't understand them, is a question I would like to see answered. Some post-election survey data and analysis would be nice, but what is clear is that they didn't fatally wound him with the Republican base, which definitely reflects movement from recent election cycles. To what degree the success of Trump has permanently altered the Republican message cluster and changed the sensibilities of its base remains to be seen, but the trend is hopeful for dovish Republicans who have counseled restraint in foreign policy against the hawkish tide.