The short-term surge in support for Biden is similar to that experienced by Sanders and Sen. Kamala Harris (D-Calif.) amid their campaign launches earlier this year.

Announcement bumps have not necessarily had staying power as the field of candidates has widened.

Harris, for example, saw a 5-point increase in her first-choice vote share after she launched her bid, but has lost much of that nationwide interest in the 12 weeks since. Six percent of Democratic primary voters supported her before her campaign launch, just one point less than the share who back her now.

And Sanders, who also saw a 6-point bump, has flattened out since, though he remains the clear second choice with 22 percent of the vote, 1 point higher than the share before he announced.

Others, such as Pete Buttigieg, saw nominal impacts in their first-choice vote share following their announcements, though the mayor of South Bend, Ind., has presided over a consistent uptick in support following other big moments in his campaign during the past several weeks that is unmatched by other candidates.