Trump calls any potential opponent names, so that Nazi comment means nothing. I see numerous similarities between Trump and Buchanan, and Paul—anti-immigration, anti-war, anti-tax, anti-foreign aid.
You are looking at Trump politics since about 2015 and today, not during his lifetime before that, and as far as his despising Buchanan, go back and look at what he thought of him back then, remember that Trump switched to the Democrat Party in 2001 after 2 years as a registered Independence Party member.