HERE'S a new one for you: an American election in which the problem wasn't too much money, but not enough.

Yesterday's dismally low voter turnout in Philadelphia - roughly 21 percent - is at least somewhat the fault of a lack of TV and radio commercials that might have rallied voters to come out.

And for that you can blame the lack of a serious challenge to Mayor Nutter - opposed only by recent tax dodger Milton Street - and for that you can partly blame money, too: specifically, a quirk in the city's campaign-finance law that makes it hard for a challenger to raise enough cash in a short time to take on an incumbent mayor.

"Unfortunately, money is what creates a profile in political races," said Larry Ceisler, a longtime local pundit, noting that candidates in hotly contested races for five open City Council seats or for city commissioner just couldn't raise enough cash to wake up a slumbering electorate the way a high-profile mayoral challenge would.

Turnout wasn't much better in the Philadelphia suburbs. The 2011 local primaries were nothing like last fall's national election - when ads paid for by big corporations and unions took control of your TV - or 2007's, when a megabucks failed primary challenge by millionaire Tom Knox raised voter awareness and turnout in an open mayoral race.

With 95 percent of the vote counted last night, the 21 percent turnout fell far short of the 39 percent of registered Democrats who turned out for the 2007 Democratic primary won by Nutter.

The irony is that - despite the big fizzle at the top of the ballot - this election will likely influence the future political direction of the city more than most, thanks to the large turnover in City Council, including the retirement of longtime Council President Anna Verna. The sweeping Council changes were largely the result of turmoil over the costly pension benefit known as DROP.

Many of those key races were decided by a thimbleful of votes.

Another contest with major implications - a primary battle for the soul of Philadelphia's shrunken Republican Party between reformers and the old guard tied to the Meehan family dynasty - was decided by fewer folks than come out for a midweek 76ers-Timberwolves game.

Why no Nutter foe?

The biggest mystery of 2011 was why no major Democrat surfaced to challenge Nutter, considering that in February his approval rating was an OK-but-not-great 53 percent and that many residents believe that the city is on the wrong track.

Political experts said that potential big-name rivals - including Knox, Councilman Bill Green, state Sen. Anthony Williams and a party-switching Sam Katz - stayed away for a variety of reasons, but money was clearly a major factor.

Ellen Mattleman Kaplan, vice president of the political watchdog group Committee of Seventy, said Nutter was boosted by a quirk in the campaign-finance law he helped write when he was on Council. The limits on donors - $2,600 for individuals and $10,600 for political committees - are for each calendar year, not for an election cycle. That means that Nutter started amassing his war chest when he took office in 2008, and late-arriving challengers could not easily catch up.

"Most people don't want to start campaigning against the mayor in 2008. They want to wait until 2010, so the incumbent has a big head start," Kaplan said. She noted that the Committee of Seventy has been lobbying to change the limits to an election cycle, which would level the playing field.

Kaplan also said Philadelphia's unusual resign-to-run rule may have persuaded incumbents like Green or City Controller Alan Butkovitz to hold on to their jobs and wait until 2015, when the mayoral race will be wide open.

G. Terry Madonna, a political scientist and pollster from Franklin and Marshall College, cited another problem: recession-battered city voters may believe it doesn't make much difference who is in City Hall.

He said that there seemed to be no defining issue in the 2011 race and that one huge local headache - failing public schools - isn't even controlled by Nutter, but by a state commission.

"What would drive turnout when there's no transcendent issue?" he asked.

Maybe a celebrity? After all, look at all the attention that real-estate billionaire and TV reality star Donald Trump brought to the GOP presidential primary during his brief flirtation, before his would-be campaign collapsed amid the President Obama birth-certificate nonsense.

Some political watchers pointed to yesterday's rainy weather, although in truth it was mostly just a light drizzle on an Election Day in which bright sunshine wouldn't have changed the outcome very much.

In a world fueled by star power, a mayoral race between a no-drama incumbent and a mostly unfunded ex-convict just wasn't enough to get Philadelphia's couch potatoes to put down the remote.