The presidential “debates” proposed by the Joe Biden campaign and accepted by his chief opponent, Donald Trump, look less like a face-to-face matchup between two political contenders than competency assessments. While so rule-constrained as to offer little in the way of a test of the candidates’ mettle, the early date of the first meeting offers nervous partisans — Democrats in particular — a last opportunity to reconsider their choice of standard-bearer before party nominations are formalized.