All of the candidates at center stage on Wednesday are betting big on Iowa — putting them in competition with one another geographically, if not ideologically. Mr. Booker’s Iowa operation rivals Ms. Warren’s as the most robust of the race so far. Mr. O’Rourke’s retail-style campaign is a traditional fit for the state. And Ms. Klobuchar, who will be standing on the other side of Mr. O’Rourke, is the senator from next door.
The six candidates closest to the center of the stage on that first night will also feature some of the ascendant diversity of the Democratic Party: three women, including the first Hindu member of Congress, as well as a Latino and an African-American candidate.
And the wide-angle camera shots will offer an additional interesting visual: the four spots at the outermost edges of the stage will all be occupied by white male candidates.
The prime-time matchup on Thursday will feature Mr. Biden, 76, and Mr. Sanders, 77 — the two oldest and (mostly) highest-polling politicians in the race — standing side by side. Of all the candidates, Mr. Sanders has been most eager to strike contrasts with Mr. Biden on policy matters since the former vice president entered the race in late April.
Now, he will get a chance to do so at close range, and there are a suite of issues on which Mr. Sanders has signaled he plans to draw distinctions with Mr. Biden, from their votes on the Iraq war to trade deals to their differing approaches to health care.
Those elder statesmen, who have each held elective office for decades, will be flanked by a pair of candidates making the case for a new generation of leadership: Ms. Harris, 54, and Mr. Buttigieg, 37, who has made the fact that he will be the same age as President Trump in 2054 a repeated joke on the campaign trial.
Those four are expected to soak up much of the attention and camera time.
For Mr. Sanders, Ms. Warren’s absence on the second night will allow him to pitch his more progressive vision relatively unimpeded. None of the other three leading candidates are likely to jostle with him for the most committed ideological voters on the left.