There are plenty of good answers to this question. Some speak to the basic political reality of national crises and some to Mr. Biden’s particular quirks.

First, the basics: In times of upheaval — be it a war, terrorist attack, hurricane or pandemic — the commander in chief commands center stage. No matter how ill equipped a president may be, he is the nation’s daddy figure, and anxious Americans look to him for guidance and action.

Political challengers must tread carefully. They can offer alternative visions, but they cannot come across as second-guessing the president’s every move from the safety of their rec rooms. If an opponent hits too hard too often, he risks looking as though he’s playing politics while Americans are dying.

Mr. Biden is in an even more delicate spot than some of his former primary rivals. He is not a governor, a member of Congress, a mayor or even a school superintendent. He has a platform but no authority. What he can essentially do is criticize and opine about how things should be done — how he would do things — if only.

Team Biden is in fact doing a lot of this, through statements, surrogates, social media and other avenues. Before Mr. Trump’s briefings, the Biden campaign sends out “Key Questions for Donald Trump” to reporters, focused on the topics du jour: why the head of the agency tasked with finding a coronavirus vaccine was removed; what is being done to address a potential shortage of coronavirus tests; why publicly traded companies are receiving relief funding earmarked for small businesses. Post-briefing, the team sends out Mr. Biden’s response.