It's from February, but just noticing what may be the first poll with who-would-you-vote-for and favorables/unfavorables for many of the potential candidates https://capitolfax.com/2025/02/24/poll-mayor-johnsons-re-elect-in-crowded-field-is-8-percent-just-7-percent-view-him-favorably-80-percent-unfavorably/

https://www.nbcchicago.com/news/local/with-2-years-left-in-mayor-johnsons-first-term-notable-names-considering-a-run-to-unseat-him/3718331/ tv analysts on the above poll (probably, I don't think it is named)

With 2 years left in Mayor Johnson's first term, notable names considering a run to unseat him

Just two years into Brandon Johnson’s first term as Chicago's mayor, challengers are already quietly testing potential runs to unseat him in 2027.

However https://www.politico.com/news/magazine/2025/03/12/rahm-emmanuel-president-2028-column-00224241

https://www.cbsnews.com/chicago/news/rahm-emanuel-suggests-run-for-mayor-of-chicago-again/

Adding Luis Gutiérrez based on https://www.chicagomag.com/chicago-magazine/march-2025/who-will-be-our-next-mayor/

Buzz around Emanuel, see https://www.politico.com/newsletters/illinois-playbook/2024/12/04/rahm-takes-the-stage-00192532 and two linked NYT pieces, as possible DNC chair, or governor, or senator, but no mention of mayoral repeat attempt.

More https://www.politico.com/newsletters/illinois-playbook/2024/11/20/booze-tax-a-buzz-kill-00190582

Adding names mentioned in https://www.chicagobusiness.com/politics/challengers-start-circling-brandon-johnson-greg-hinz