Traditionally, American presidents (of both political parties) have divested themselves of business interests before taking office. This allows them to consider only what they think is best for the country when they make both foreign and domestic policy decisions (without people thinking they were just trying to enhance their own businesses).
We can debate whether those decisions were actually good for the country, but there is no belief that they were just trying to make themselves richer by their policy decision.
Donald Trump is different. He refused to divest himself of his businesses, and some of his policy decisions have made himself much richer -- such as his tax cuts (which favored the rich and corporations). Trump and his businesses have benefitted greatly from that law.
And the same goes for foreign policy decisions. He has been very friendly toward the murderous regimes in Russia and Saudi Arabia. He has tried to make it sound like that was good for the country, but most people aren't buying that. They believe he is acting in his own best interests -- not the interests of this country.
A new poll shows that, by a 15 point margin, people think the policy toward Russia is affected by Trump's business interests (54% to 39%). And by a 23 point margin, people think policy toward Saudi Arabia is affected by Trump's business interests.
The charts above use information in a recent Quinnipiac University Poll -- done between December 12th and 17th of a national sample of 1,147 voters, with a 3.4 point margin of error.