Quite apart from raising a question about the flexibility of Donald Trump's relationship to the truth, an article in the Washington Post also raises questions about the ethics of his legal team. According to the Washington Post, Trump justified his lawsuit against New York Times reporter and Trump biographer Timothy O'Brien because it would cost the reporter money to defend:
In a brief statement this week, Trump said he felt the lawsuit was a success, despite his loss.
“O’Brien knows nothing about me,” Trump said. “His book was a total failure and ultimately I had great success doing what I wanted to do — costing this third rate reporter a lot of legal fees.”
Trump: A True Story, Washington Post, Aug. 10, 2016 (last accessed Aug. 10, 2016)
I don't have any idea who Trump's attorney is, but it would be a shame if he is still in practice. Attorneys who bring frivolous lawsuits mainly for the purpose of driving up the other side's attorney fees and expenses are violating both the law and professional ethics. Moreover, the court has the power to make the attorney pay for the other side's excess fees and costs:
Any attorney or other person admitted to conduct cases in any court of the United States or any Territory thereof who so multiplies the proceedings in any case unreasonably and vexatiously may be required by the court to satisfy personally the excess costs, expenses, and attorneys’ fees reasonably incurred because of such conduct.
Moreover, the Bar also prohibits the filing of frivolous lawsuits:
A lawyer shall not bring or defend a proceeding, or assert or controvert an issue therein, unless there is a basis in law and fact for doing so that is not frivolous, which includes a good faith argument for an extension, modification or reversal of existing law.
Maybe Donald Trump knew no better, but his lawyer should have.