In recent cycles, the debates have been enough to bring more attention to some candidates and put them into contention. That was the case in 2012, for instance, for Herman Cain and Newt Gingrich. A few candidates, like Rick Perry or Scott Walker, stumbled in the debates and never recovered.

But more often, the debates have a far more modest effect, and it is important to have some perspective. A shift in support is likely to be fleeting, not a lasting change in the race.

You might feel that many candidates this cycle have already faltered, even if not as dramatically as Mr. Perry did with his “oops” moment. Beto O’Rourke or Kamala Harris, for instance, enjoyed initial success but have slipped back in the polls.

But sometimes even those who fall into a steep decline can pull out of it, like John McCain in 2008. Mr. O’Rourke and Ms. Harris still possess the traits that made them intriguing to Democrats, and could easily claw back, for example.

Elizabeth Warren has already done something like what Ms. Harris and Mr. O’Rourke might hope to do. She struggled early on, in part because of questions about her electability and the way she handled a DNA test on her claim to Native American heritage. But she has since recovered, and more, going on to deliver a steady stream of policy proposals.

If Ms. Warren winds up advancing to the nomination, perhaps we’ll remember it the way we remember Donald J. Trump’s rise in 2016 or Barack Obama’s in 2008.

But for now, she is at just about 12 percent in an average of national polls — about the same support she had shortly after her announcement, a few points behind Bernie Sanders today and a few points higher than Mr. Buttigieg or Mr. O’Rourke at their peaks. Her level of support is less than what Mr. Walker had heading into the first Republican debate; he was out of the race less than two months later.

She and other leading candidates may have the spotlight now, but a lesser-known candidate could succeed in prying it away from them in the debates this week, joining Mr. Buttigieg in becoming a more familiar face to Americans.