He has told aides that he hopes the trip, which includes a stop in Aberdeen on Saturday, will provide a much-needed “reset” for his campaign. But some of the aides have said privately that they wished he would cancel it.  Mr. Trump’s self-image as a successful businessman is important to him, and, even though he has said publicly that he is relying more on his children to run the Trump Organization nowadays, he remains closely tied to it. He also believes that many of his supporters are drawn to his persona of a brash billionaire, born out of his decades in the business world.  He does not like to be away from his business operations for long. Save for just over a dozen nights during the primaries, he has returned to one of his homes at the end of each day, usually to his New York City apartment, which allows him access to his 26th-floor office in Trump Tower, where he works and takes part in interviews.  And he tends to rely on Trump-connected businesses while he is campaigning, further bringing together the two worlds in which he operates.  Perhaps the most stark example of his business empire intruding on his political career came late last month. Mr. Trump delivered scathing criticism of Judge Gonzalo P. Curiel — first at a San Diego rally and then again in interviews — that was less a result of a politically strategic calculation than of Mr. Trump’s concerns about rulings the judge made in a federal lawsuit against his now defunct Trump University.  Mr. Trump accused the Indiana-born judge of being unable to render fair rulings because of his “Mexican heritage.’’ The political backlash was swift, with many of Mr. Trump’s supporters distancing themselves from him and calling his comments racist.  What’s next for a campaign with a big fund-raising gap.  The Scotland trip, too, is potentially fraught. Since clinching the Republican nomination, Mr. Trump has squandered numerous opportunities to unify the Republican Party behind him, or exhibit the discipline party leaders and donors are eager to see.  When Barack Obama headed to Europe as a presidential candidate in 2008, and Mitt Romney, the 2012 Republican nominee, traveled to England, Israel and Poland during his campaign, both men went to demonstrate their global savvy and stature, in meticulously planned visits. (Mr. Romney’s trip, nonetheless, was a gaffe-ridden disaster and many of his aides later said they wished he had stayed home.)  “Foreign trips are an inherently risky endeavor,” said Lanhee Chen, a fellow at the Hoover Institution who advised Mr. Romney in 2012. “Ideally, they will boost a candidate’s credibility on and familiarity with the geopolitical issues of the region they visit. But they require a lot of planning and logistical coordination. Seems to me that a foreign trip driven solely by personal financial interests — as Trump seems to be planning later this week — would be unprecedented.”  Showing up right after the Brexit vote, in the middle of a tumultuous time, is leaving Mr. Trump especially vulnerable to criticism, as well as creating the potential for an international blunder.  When asked about the vote in an interview this month with The Hollywood Reporter, Mr. Trump seemed not to be familiar with Britain’s referendum, first answering, “Huh?” and then, “Hmm.” Finally, after the Brexit vote was explained to him, Mr. Trump answered with his trademark decisiveness: “Oh yeah, I think they should leave,” he said, a sentiment he has since repeated. On Wednesday morning, however, Mr. Trump told Fox Business that his opinion on the issue was not significant since he had not followed it closely.  But business has always been inextricably bound with politics for Mr. Trump, dating back to his previous flirtations with presidential bids, which served largely to elevate his public profile and business interests.  The latest documents submitted to the Federal Election Commission, for instance, show that Mr. Trump paid at least $1.1 million in May to his business and family members for campaign-related expenses. The largest payment, for $423,000, went to his Mar-a-Lago Club, for the use of that private Florida resort, but he also reimbursed costs associated with his private airplanes, Trump Restaurants, and even Trump Tower, which houses his campaign headquarters on the fifth floor.  “Why would I use someone else’s properties?” Mr. Trump said, through Hope Hicks, a campaign spokeswoman, in response to a question about why he had hosted campaign events at his properties.  “Mr. Trump owns some of the finest properties anywhere in the world and he has to host events, news conferences, etc. which might as well be hosted at those properties,” Ms. Hicks added, in an email statement. “They are paid, in accordance with F.E.C. regulations, their approximate fair market value for goods and services.”  Mr. Trump also sometimes reserves the front rows at his news conferences for members of his private clubs, almost as a membership perk.  And at a primary election event in March at Trump National Golf Club in Jupiter, Fla., Mr. Trump spoke flanked by bottles (and cases) of Trump-branded wine, Trump-branded water, and a mound of raw steaks, which he tried to pass off as his brand.  Even Mr. Trump’s private 757, emblazoned with his name across the side and a tool for his businesses, now occupies a central role in his campaign imagery, rolling up to airport hangars during primary rallies as a symbol of power and success. People in the crowd gawk in awe, pointing to the plane, unprompted, as a reason they believe in Mr. Trump.  Yet some Republicans still think Mr. Trump should simply disentangle the personal (and business) from the political.  Mr. Chen, for instance, had a suggestion for Mr. Trump’s trip: “If he’s going to Europe anyway,” he asked, “why not take some time to visit with the NATO allies that would be affected by his plan to pull back on the U.S. commitment to the organization?”
Presidential contenders usually try to burnish their foreign policy credentials when abroad. Mr. Trump plans no meetings with government or political leaders.