Now that the once-sprawling field of Democrats seeking the presidency has become a two-man race, many in the party are breathing a sigh of relief. All the more so because Joe Biden is the clear front-runner and the dreaded Bernie Sanders looks to be fading. So it’s all set. Biden will be the nominee and give the party a solid chance of scoring a November trifecta: beating President Trump, taking the Senate and holding the House. Count me as skeptical. Instead of a smooth ride, it’s more likely that the Dems’ desperate search for a Trump slayer will hit more...