And then there were 21 … candidates to succeed former Rep. Jesse L. Jackson Jr., D-Ill.

This afternoon, former NFL linebacker Napoleon Harris dropped out of the 2nd District special election and backed fellow Democrat, Cook County Chief Administrative Officer Robin Kelly.

“I believe we need to fight for more educational opportunity, better jobs and to get guns out of the hands of criminals and gangs that are preying on our neighborhoods,” Harris said in a statement from the Kelly campaign. “I believe Robin Kelly is the right candidate to pick up that cause to fight for the people of Chicago and the Southland.”

While the Democratic field remains large and varied, Kelly’s supporters argue this helps her because it puts more of Harris’ geographic base — including the key Thornton Township — in play.

The top tier of candidates includes Alderman Anthony Beale, former Rep. Debbie Halvorson, state Sen. Toi Hutchinson and Kelly. The Feb. 26 Democratic primary winner is expected to come to Congress given the district’s heavy Democratic composition.

Recent polls have shown Halvorson with a small lead. She boasts strong name identification in the district from challenging Jackson in the primary last year, although Halvorson lost badly.

That could change soon. New York Mayor Michael Bloomberg’s Independence USA PAC has targeted Halvorson with a major media buy hitting her previous support for gun rights. It’s an important issue in Chicago, which has experienced an increase in gun violence recently.

The ad buy is for $375,000 on cable and broadcast markets in Chicago through Feb. 3, according to a source who tracks media buys and is not affiliated with the PAC.

The advertisement is also notable because none of the candidates have enough funds to air television spots yet — and they might not in the remaining weeks before the primary.

Abby Livingston contributed to this report.