Some of the lessons are specific to Trump's coalition, which, at the moment, looks badly outnumbered against the Americans who view him unfavorably. Others apply more broadly. They emerge from public opinion polling, from election patterns, from viewing habits.
They are the ingredients — mixed together with widespread frustration with Washington and an unusual (to say the least) string of political events this primary season — that have vaulted Trump to the general election and possibly the White House.
1. Racial tension remains high
Seven years after America elected its first black president, racial animosities surged to the center of this primary season. Trump fanned them from the start, saying many Mexicans who immigrate illegally to the United States were rapists and drug dealers. He retweeted white supremacists and struggled to disavow the endorsement of former Ku Klux Klan grand wizard David Duke.
Among the public overall, 40 percent say blacks losing out due to preferences for whites is the bigger problem facing the country while 28 percent say whites losing out is the bigger problem. That means more than two-thirds of Americans still see a damaging level of racial prejudice in the country, one way or the other.
2. Globalization is scary
Trump's two most effective policy arguments in the campaign have both channeled the anxieties of an America increasingly open to the outside world. His promises to deport all immigrants here illegally helped distinguish him from his GOP rivals early on. His pledge to build a wall on the Mexican border, and to make Mexico pay for it, has become a stump-speech staple. So has his blistering critique of U.S. trade policy and his promises to "win" with China, bringing back manufacturing jobs that were outsourced over the last two decades.
Rust Belt politicians have railed against trade for years. Conservative Republicans, including 2012 GOP nominee Mitt Romney, have taken increasingly hard lines on immigration. No presidential candidate has ever united the issues as effectively as Trump. Two-thirds of his supporters say trade deals have been bad for the United States, according to Pew, a staggeringly high number for the presumptive nominee of the party that most often espouses free trade and markets as a key to growth and prosperity.
The appeal could resonate in the general electorate, too, particularly in states hit hard by outsourcing in the past. Polls show Americans remain split on trade overall — Pew finds slightly more support for them than opposition — but exit polls showed lopsided disapproval of trade deals in Michigan, for example, on both the Republican and Democratic side.
3. There's deep hostility to Muslim refugees
Raise your hand if you predicted Trump's call to exclude all the members of the world's second-largest religious group from entering the United States would prove hugely successful in the primaries — and draw support from a third of Americans overall, per Post-ABC polling.
In the wake of mass killings carried out by Muslims in Europe and in California over the last year, however, Americans have grown wary of allowing Islamic immigrants, or even simply visitors, into the country. That's particularly true for Republicans. Last fall, a majority of GOP voters told Post-ABC pollsters that they opposed taking in refugees from Syria or other countries in the Middle East, even after screening them for security purposes.
4. Celebrity culture dominates
Since he announced for president, Trump has been mentioned on cable news nearly 500,000 times. That's not quite as much as every other candidate for the White House combined, Republican and Democrat, but it's close. Hillary Clinton, in second place, has been mentioned 200,000 times.
Networks keep airing Trump because people keep watching him, and not just his supporters. At a time when American viewing habits are increasingly fractured, he alone has solved a Rubik's Cube of star power, controversy and surprise to command cameras at every turn. He is the first master candidate of the reality TV era, and his dominance amounted to a huge financial advantage on his rivals. Speaking of ...
5. Our votes can't always be bought
Remember when Jeb Bush's $100 million Super PAC made him inevitable? Right. There's plenty of evidence that campaign spending often influences who wins elections. But Trump, who spent far less than Bush, Ted Cruz or any of his other serious rivals, shows voters sometimes can't be swayed by big money.
Scott Clement contributed.