It took 3 years for George W. Bush to hit 50% disapproval. Trump is there after 8 days.
Nearly every modern president has, at one time or another, reached the point at which at least 50 percent of the country disapproved of his job performance as president. For Donald Trump, though, that moment has come earlier than most much earlier.
While Trump entered office with record-low approval, he now stands at a dismal 42 percent approval, according to a Gallup poll of 1,500 Americans released January 28. The same poll showed that just eight days into his presidency, 51 percent of those surveyed do not approve of Trump's job in office. Perhaps using his first week to begin construction of a border wall, halt refugee immigration from seven majority-Muslim countries, announce plans to roll back the Affordable Care Act, and reinstate a "global gag rule" around abortion may have had something to do with it.
http://www.cnbc.com/2017/01/30/pols-trump-reaches-majority-disapproval-faster-than-any-modern-potus.html