Frank Rizzo to become Democrat, may run for mayor in 2015

* UPDATED BELOW WITH KNOX's WITHDRAWAL FROM RACE

Former City Councilman Frank Rizzo, who served as a Republican but then changed to independent after losing the 2011 primary for reelection, says he will become a Democrat on Monday in anticipation of running for mayor in 2015.

The location and timing of Rizzo's political conversion is interesting: He's doing it at the Philadelphia City Committee office of U.S. Rep. Bob Brady, the city's Democratic chairman.  Rizzo says Brady is being "very courteous to me" but that doesn't add up to any kind of endorsement.

There are a few factors to keep in mind here.  Brady has been pretty clear about his support for state Sen. Anthony Hardy Williams, an African-American from West Philly who is expected to run for mayor in 2015.  Brady is not a big fan of Tom Knox, a white Center City millionaire who will announce his candidacy for mayor on Wednesday. Knox finished second in the 2007 Democratic primary for mayor after tangling with Brady in that race.

In the racial math so often used for Philadelphia citywide races, a white competitor for Knox could help Williams.  Rizzo says it's too soon to say if that matters since the entire field of candidates is still not known.  He also said his change in party registration is not meant to "preempt" Knox's announcement.

Rizzo served four terms but was tripped up politically because of his participation in the controversial Deferred Retirement Option Plan, known as DROP, which allowed some elected officials to retired for one day, collect a six-figure pay-out and then go back to work when elected to a new term.

Now retired, Rizzo said he planned to announce after the holidays if he will run for mayor. He noted that he and his father, the late Mayor Frank Rizzo, still have a strong political brand for a last name.

"I was raised by a mayor, who will always be revered in Philadelphia as doing a good job," Rizzo said. "I watched him work. I utilized some of those things saw when I was in City Council."

* UPDATE: Tom Knox just withdrew from the 2015 race for mayor this afternoon.