Chicago mayoral race: Why some of the 15 candidates could be knocked off the ballot

Fifteen candidates are challenging Brandon Johnson for his job as Chicago mayor, but the field may not stay that crowded.Race for Chicago mayor heats upThe city's petition objection period began Tuesday, opening the door to what can become a costly and politically strategic fight over who ultimately makes the ballot.Chicago mayoral candidates are required to collect at least 12,500 valid signatures to qualify for the ballot.Most of the major candidates say they submitted far more than the minimum, with Alexi Giannoulias submitting about 60,000 signatures. But opponents can now challenge those signatures one by one.Signatures can be challenged for several reasons, including if the signer is not a registered Chicago voter, signed more than once or used an address that does not match voter records. Challenges can also target errors in the petition paperwork itself.Election officials review disputed signatures and determine whether a candidate still has enough valid signatures to remain on