Donald Trump on Saturday was fact-checked live by a NBC News reporter who was attending the former president’s Iowa rally. Trump said at his rally that the Civil War, and therefore the existence of slavery as an institution, should have been “negotiated,” instead of erupting in bloodshed. He also said that no one would have ever heard of Abraham Lincoln had he simply negotiated the conflict between slave states and non-slave states. Trump’s comments were mocked by fellow conservatives, lawyers, and historians. POLL: Should Trump be allowed to run for office? But right after Trump made the cont…