The election is, in fact, Wednesday, as President Obama noted five times in a video he released Monday on behalf of the Democrat in the race, Mayor Cory A. Booker of Newark.

Polls open at 6 a.m. and close at 8 p.m.

Mr. Booker, mayor of the state’s largest city, with a Twitter following six times its population, has tried in the final days to make the special election a referendum on the government shutdown, casting his Republican opponent, Steve Lonegan, as a Tea Party obstructionist.