Dynamic Joe Biden takes command in making his case to an America in crisis

(A heavier lift on the cognitive-agility front awaits late next month, when the presidential debates begin, and in unscripted interviews.) But in this speech, billed as the candidate's biggest in nearly a half-century of politics and a decades-long pursuit of the White House, Biden displayed a command of his material and an emotional dynamism as if he could hear a packed convention hall cheering.The second challenge was to convince viewers that he could do a better job than President Donald Trump in battling the coronavirus pandemic that has killed nearly 175,000 Americans, shattered the economy and upended everyday life, producing this year's "unconventional" conventions, shorn of balloon drops and delegates in funny costumes.Without referring to Trump by name, the Democratic nominee called out the president for failing to plan or take the virus seriously.