With several Democrats openly floating the possibility they might vote to acquit President Trump, congressional Republicans are planning an aggressive "Plan B" strategy in the event some Republicans break off and demand additional witnesses in the president's impeachment trial, Fox News has learned. Senate Majority Leader Mitch McConnell, R-Ky., privately said early Tuesday that he wasn't sure there were enough Republican votes to block more witnesses, given that some moderates in the GOP's 53-47 Senate majority were wavering. Any witness resolution would likely require four Republican defections in the Senate, because in the event of a 50-50 tie, Chief Justice...