WASHINGTON — President Barack Obama fiercely rejected Donald Trump’s depiction of an America in crisis on Friday, arguing that violent crime and illegal immigration have plunged under his leadership to their lowest rates in decades. Looking to November’s election, Obama said, “We’re not going to make good decisions based on fears that don’t have a basis in fact.” At a news conference alongside Mexico’s president, Obama sought to undermine two pillars of Trump’s speech Thursday night in which he accepted the Republican presidential nomination.