HOUSE OVERSIGHT 020444 Steve Bannon believes the specter of impeachment will motivate mainstream Republicans as well as core Trump backers. Photo: J. Scott Applewhite/Associated Press "This is all grass roots," Mr. Bannon says. "It's 2016 all over again...This is Trump's first re-election." The political calculus behind such thinking is pretty simple: In 19 months as president, Mr. Trump has hardened his grip on his base of supporters and the GOP overall, but has done little to expand that base. Meanwhile, as the Labor Day kickoff of the fall campaign approaches, Republicans face a Democratic party whose activists appear exceptionally motivated—to campaign, donate money and turn out in November. Republicans need something to match that fervor. That something is the Trump base—and the best motivating tools are anger and fear. In this case, that means specifically the fear that Special Counsel Robert Mueller, New York prosecutors and a Democratic Congress will conspire to kick Mr. Trump out of office. That's why Republicans are talking about the specter of impeachment, not Democrats. Democrats know impeachment talk is a surefire way to motivate the other side. But there's a problem in this GOP formula: A motivated Trump base is necessary for Republicans to head off disaster in November, but it's not sufficient, at least not if Democrats remain as energized as they appear today. The Trump base has to be married with more mainstream Republicans—the kind hardcore activists refer to as RIN0s, or "Republicans In Name Only"—and with some independent voters. Right now, independent voters are hard to read. Their sentiments have been shifting around a lot in Wall Street Journal/NBC News polling in recent months. As a general rule, they have a low regard for Mr. Trump personally and appear weary of the atmosphere of constant crisis around him. But the polling also indicates they increasingly like how Republicans are handling the economy, appreciate the GOP t