So far at least, nothing really has. Trump survived questioning John McCain's war hero status, proposing a ban on Muslims entering the United States and basically shredding all previous notions of decorum on the campaign trail, hurling crude insults at anyone who criticized him. He likened Ben Carson to a child molester. He later won Carson's full endorsement.
But Trump is entering a different arena in which he will have to convince a much larger audience than the one he commanded in the primaries. Thus far, Trump has won close to 11 million votes. He will set a record for Republican support in a primary campaign. But to win the White House, Trump probably needs 50 million to 60 million votes. And he will need to appeal to women and minority voters to carry swing states like Florida, Ohio and Virginia.
Trump already has an enormous climb ahead of him to even limit his losses among these voters. He has a 70 percent negative rating among women and fares even worse with African-Americans and Latinos. Hillary Clinton has very high negatives as well but does far better than Trump with women and minorities.
And a poll over the weekend showed Clinton running close to even with Trump in Georgia, a state Democrats haven't carried since Bill Clinton did it in 1992.
If Clinton can peel off states like Georgia and North Carolina, Trump stands almost no chance. A generic Democratic presidential candidate begins the presidential race with 190 safe Electoral College votes out of the 270 needed to win and another 57 that lean heavily to the Democrats.
If Clinton simply holds these states she would need just 23 more electoral votes to win. And at the moment, there are 100 more electoral votes that lean Democratic, including Ohio and Florida. Clinton could even lose Ohio and Florida and still win if she cobbles together a few other smaller states such as Virginia and Colorado. You can play with the electoral map for yourself and you will quickly see how tough the road is for Trump.