I chuckled and lamented all at once when you wrote this bit of history and advice:

"As it happens, President Roosevelt gave this speech at the 1941 White House Correspondents Dinner, which took place four days after the Lend Lease vote. This year’s White House Correspondents Dinner is Saturday. But I wouldn’t follow FDR’s example in this respect. Biden, I suspect, should speak directly to the nation. From the Oval Office. Or perhaps from the FDR Memorial, which includes a quotation from his Lend Lease speech."

In fact, FDR was speaking to the nation when he spoke to the press at the WH Correspondents Dinner, because more people read newspapers in those days. In fact, more people probably could read back then. And radio news wasn't polluted and overrun by right wing pundits reinterpreting the meaning and parsing every clause to distort and belittle.