WASHINGTON — Florida Gov. Rick Scott will run for Senate, a Scott political adviser confirmed to NBC News on Monday, challenging longtime incumbent Democrat Sen. Bill Nelson and turning up the heat in what will be one of the nation's most-watched midterm election battles. Scott's move sets up a contentious and pricey battle for Democrats to defend the seat they've held for almost two decades, but also brings President Donald Trump's possible impact on down-ballot races into close focus yet again. The president has been urging Scott — a key supporter of Trump for president in 2016 — for months...