Congress will formally count electoral votes for president on Jan. 6. Here’s what you need to know.

The 2020 presidential election cycle is almost over. After the voting, the counting, the legal challenges, and the casting of the electoral college votes in December, a joint session of Congress will formally count the electoral votes for president at 1 p.m. on Jan. 6. The final margin — 306 for Joe Biden and 232 for Donald Trump — is already known.

Normally, it would be a day of pomp and ceremony. But this year, continuing efforts by Trump and his supporters to overturn the election result will make the...