John Harwood talks with Sen. Mark Warner of Virginia, a Democrat suddenly back in the national spotlight as he helps lead the Senate’s Trump-Russia investigation. Once considered a presidential contender, Warner could be back in the mix for his party’s 2020 nomination. They discuss his belief that the notorious “dossier” hasn’t yet been disproven, that Trump campaign contacts with Russia turned out to be far more numerous than expected, and that firing Special Prosecutor Robert Mueller would provoke a constitutional crisis and political disaster for the president. He condemned GOP tax proposals as the worst legislation he’s ever seen, and talks of new proposals for a 21st century economy that could represent a White House platform.