He hasn’t even said he’s running, but former Vice President Joe Biden keeps coming in first in polls asking Democrats to name their preferred presidential candidate for 2020.

The latest comes from a Des Moines Register/CNN/Mediacom Iowa Poll of likely Democratic caucus-goers, which has him again beating out Vermont Sen. Bernie Sanders for the top spot. Perhaps even more significant, when Iowa Democrats are asked whether the candidate’s views are “too liberal” or “too conservative,” 70% say Mr. Biden’s are “about right”—well...