Washington - The ghostwriter who penned Donald Trump's 1987 memoir "The Art of the Deal" thinks the US president will throw in the towel before the end of his term.Writer Tony Schwartz tweeted that "Trump is going to resign" before investigators probing alleged ties between the Republican's campaign team and Russia "leave him no choice"."The circle is closing at blinding speed," the author tweeted. "Trump is going to resign and declare victory before Mueller and congress leave him no choice.""Trump's presidency is effectively over," he said in a follow-up tweet. "Would be amazed if he survives till end of the year. More likely resigns by fall, if not sooner."While writing Trump's bestselling breakthrough memoir, Schwartz spent 18 months with the billionaire tycoon.He spoke out last year against the real estate mogul during the presidential campaign, telling The New Yorker magazine that he put "lipstick on a pig"."I feel a deep sense of remorse that I contributed to presenting Trump in a way that brought him wider attention and made him more appealing than he is."