IT'S NEARLY IMPOSSIBLE to oust an incumbent Philly state lawmaker.

About the only time one leaves is to collect a fat, taxpayer-paid pension, go to prison or, as in the case of Rep. Tony Payton, (unbelievably) fail to get the minimum 300 signatures needed to run.

So a good political rule of thumb in the City of Brotherly Love is once you're in, you're likely in for about as long as your want.

That rule's being ignored by 31-year old community activist Numa St. Louis (pronounced Sawn Louee). He's challenging forever-incumbent Rep. Mark Cohen in Tuesday's primary.

Cohen, 62, represents North Philly's 202nd District, which runs from Ogontz to Rhawnhurst and is gerrymandered to look like a snake.

Cohen's been in office since 1974, when Richard Nixon was president and Bernie Parent was MVP, when the Flyers beat the Bruins to win the Stanley Cup.

Cohen rarely has an opponent. Last time he had a primary was 1984. Last time he was opposed in a general election was 2004, and he won with 79 percent of the vote.

This is not uncommon. This year, 10 Philly lawmakers have no opposition in primary OR general elections.

And so it goes.

But St. Louis, who's worked for homeless youth and immigrant rights, is running because, he says, "I believe the district has a great deal of potential" for economic growth and because Cohen "has not been pro-active in bringing home the bacon for jobs or improving public safety or schools."

He stresses improving areas around SEPTA transit centers and says stations at Broad and Olney and at Nedro and 10th Street (Fern Rock) could be "anchors" for economic development and public-safety improvements to cash in on and better protect tens of thousands of daily commuters.

Long odds against incumbents don't deter him.

"We're doing lots of face-to-face contact," St. Louis says, "I think people are finding it refreshing that a candidate is at their door seeking their input."

At a minimum, he's forced Cohen to run a race.

"I'm actively campaigning," says Cohen. "Mailings are going out. There's a campaign office, a campaign car, T-shirts, buttons. I'm enjoying it."

Asked what he's proudest of in 38 years in office, he says, "organ-transplant legislation."

It passed in the '90s and makes access to and information about organ transplants easier. It was signed into law by Gov. Casey, himself a double-organ recipient, and was the model for national policy adopted under President Clinton.

But Cohen's incumbency isn't without controversy.

In 1990, he led all 203 lawmakers in expenses, collecting more than $104,000 over 18 months.

The expenses were permitted under House rules and included 501 "per diems" of $88 each and 162 airline tickets for flights between Harrisburg and Philly.

His claimed expenses for weekends and holidays such as Christmas, Easter, Labor Day, New Year's Day and Yom Kippur. He said he flew because "driving wears me out." (He tells me he now takes trains.)

In 2004 and 2005, he spent $28,000 in taxpayer money to buy more than 800 books. He was among the many Philly lawmakers who kept a portion of the '05 pay raise even after it was repealed. And recently he was among Philly lawmakers confessing that they didn't read but voted for a House resolution proclaiming "The Year of the Bible." He later sought, unsuccessfully, to repeal it.

When I ask Cohen why he's seeking re-election, he says, "To stand up against the policies of Tom Corbett."

Both candidates hold advanced degrees: St. Louis graduated from the State University of New York and has a master's from Temple; Cohen is a Penn grad with a law degree from Widener and an MBA from Lebanon Valley College.

Cohen is the Legislature's longest-serving member. St. Louis would be among its youngest. There is no Republican in the race.

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