What is 'public interest'?

What is 'public interest'?

Trump is trying to do politics like he has been doing business.

What is the difference between the two? 
Businesses exist to make profits, but the government is serving public interest.
But businesses for sure can simultaneously serve public interest and not everything the government does serves the interests of the entire population.

What is public good after all?
Maybe it is a good in any form that enables citizens to 'live together'.

Trump is challenging the fundamental notion of our society - data and proof.
He does not drive conclusions objectively, based on the data.
No, on the contrary he has subjective opinion that he needs to back up and he creates a data to do so.
And it is scary because you start to question the value of the data.
It is human nature. We believe in what we want to see.

But, the data is important. 
Politics is part of Social Science. 
let me repeat. Social SCIENCE.
When you say your inauguration was the most attended, you need to compare the numbers with previous ones.
When you authorize a pipeline, at least check the number of jobs it will create in the LONG-TERM (in short term only 50 jobs btw and no one knows from where you got the number 28,000)

Maybe the only way to stand against bullshit is to show the numbers, the data.
But what do you do if the other side does not believe in numbers, does not believe in the same logic that you do?