Amidst all of the criticisms levelled at Donald Trump, there is one aspect of his campaign that has largely gone unnoticed: his tendency to blur the line between the public and private spheres.When the PGA announced that it was moving its World Championship Golf tournament from the Trump-owned Doral golf course in Florida to courses in Mexico, candidate Trump told a rally, “But that's ok.  Folks, it's all going to be settled. (I)f I become your president, this stuff is all going to stop.”Trump has also threatened to take action against the judge overseeing a case against his University.  “They ought to look into Judge Curiel, because what Judge Curiel is doing is a total disgrace. Okay? But we will come back in November. Wouldn't that be wild if I am president and come back and do a civil case? …This is called life, folks.”Trump has even mused about taking aim at the First Amendment right to freedom of the press with a view to personal gain. “I'm going to open up our libel laws so when they write purposely negative and horrible and false articles, we can sue them and win lots of money.”The Brexit vote was also viewed through the lens of what it meant to Trump: “When the pound goes down, more people are coming to Turnberry”, he saidThis penchant for feathering his own nest is also on display in his campaign spending, about 20 per cent of which has been on his own properties and businesses, including his Florida resort, Mar-a-Lago, the Trump plane and Trump wine.While this might be strictly legal, it highlights how Trump has chosen to run his campaign in a way that benefits his personal holdings.So why does this conflating of the personal and private matter?  Because our democratic system depends on the distinction.  When you blur the line between personal and private, the temptation can be to act as if there is no line, creating the conditions for corruption.What's more, the private and public spheres have different responsibilities and different priorities - or they should. It's not the private sector's responsibility, for example, to act in the public interest. If a public good results from the pursuit of private interest, so much the better. But the two are not one and the same.The importance of this distinction can be traced back to democracy's earliest days. In The Republic, for example, Plato sought to avoid a conflict between private interests and public duties by having a special class of citizens, called Guardians, rule the city.  To avoid potential conflicts, Guardians could not hold private property or have families.Today, we don't demand such extreme sacrifices of our leaders, but we do insist that public office be used as a vehicle for public service, not as an extension of private lives.All of this seems to be lost on Donald Trump.  Perhaps he sees public service as simply another “deal”, to be exploited for maximum personal advantage.  If so, there might be clues to his conduct as president.How would President Trump react to adverse judicial decisions – especially if he had a personal financial stake in the outcome?   Would he use ad hominem attacks on judges to undermine judicial independence?  Would he try to intimidate the press by changing libel laws?  Or would the mere threat to do so be sufficient?Some Republicans have reassured Americans that the country's institutions would protect the country against the worst of Trump's propensities – a stunning statement on its face.  But Trump is not easily controlled.Party luminaries, from Paul Ryan to John McCain, have demonstrated the limitations of their leadership and the pliability of their principles.  Certainly Trump sees no need to change how he operates:  “You win the pennant and now you're in the World Series—you gonna change?”In a recent article, Henry Paulson Jr., former U.S. Treasury Secretary and head of Goldman Sachs, called the “Art of the Deal businessman” a “master of advantaging himself over his fellow stakeholders and partners.”The problem is that now his “fellow stakeholders and partners“ are the American people.   And that's a deal they should be careful of making.Lawson Hunter is Counsel at the national law firm, Stikeman Elliott, and a Senior Fellow at the CD Howe Institute. Earlier in his career, he was head of the federal Competition Bureau, and later served as Executive Vice President at BCE and Bell Canada.