In this episode of The Investigation, presidential candidate and US Rep. Seth Moulton (D-MA) talks about why he's ratcheting up calls for Trump's impeachment, even though it continues to be a contentious topic with his colleagues in the House and fellow 2020 contenders. "We spend too much time in this party debating the politics of impeachment, when the law is very clear and our constitutional duty is clear," Moulton says, explaining why he thinks that skimming over the topic in the lead up to the general election would be "a mistake," and why he believes that Robert Mueller's pending appearance on Capitol Hill could be a game changer. Later, the ABC team forecasts what to expect from Mueller's testimony and analyzes the political roadblocks facing congressional democrats who want to launch impeachment proceedings against Trump. Learn more about your ad choices. Visit megaphone.fm/adchoices