An excellent video that explains Trump's political emergence is entitled, "Authoritarianism: The political science that predicted Trump's rise." Trump is no Hitler, but he resembles many authoritarian leaders throughout history in that he sees himself as the authority, but not under the authority of the law.
Although he promotes many extremist policies, his politics in some other ways are more moderate than those of Sen. Ted Cruz (e.g. his comments about Planned Parenting doing many good things other than abortion regarding women's health). However, his extremism is apparent in other policy areas, and can be especially seen in his way of using power.
In contrast, President Eisenhower was a man in authority and under authority. He was the General and the Chief Executive in manner. He also saw himself under the authority of the U. S. Constitution and the American people. He was no authoritarian. This is in contrast to Trump who argues that the rules should bend to his own will. Listening to Trump speak now for several months, I conclude Trump clearly wants to be both in authority and the authority in spite of what the U. S. Constitution says.
For example, when Gov. John Kasich did not drop out the of the Republican race early this year, Trump argued that Kasich should not be allowed to run. Yes, he said "Kasich shouldn't be allowed to run. Honestly, Kasich should not be allowed to run..." ." In a free country, all qualified individuals are allowed to run for office, no one is forced to drop out until the final election results are certified. A man who understands he is under the authority of the law could say that Kasich should drop out of the race, but Trump said Kasich's liberties should be curtailed. His choice of words reveals his approach to politics: it must bend to his will.
Trump's nomination will at best set the Republican Party back by four to eight years or more, and at worse may destroy the party that once nominated such presidents as Abraham Lincoln, Theodore Roosevelt, Dwight David Eisenhower, and Ronald Reagan. What the Tea Party has not destroyed in the party of Lincoln, Trump is now finishing off.