Pennsylvania permits 30 days in jail and a $500 fine for possession of up to 30 grams of marijuana - about an ounce. (New Jersey law is stricter: up to six months and $1,000 for 50 grams or less.)
Most first-time violators get probation, Leach said. But they still land in jail if possession becomes a probation violation for another offense, or if they don't pay fines and court costs.
Philadelphia treats possession as a summary offense - a ticket. But marijuana laws are enforced in most areas of the state.
"We have spent billions of dollars [nationally] investigating, prosecuting, incarcerating, and monitoring millions of our fellow citizens who have hurt no one, damaged no property, breached no peace," Leach wrote last week in an open letter to the state's newspapers.
His marijuana bill has gained only a few Senate cosponsors. If it somehow passed in the legislature, Gov. Corbett has vowed he would veto it, saying marijuana is a "gateway" to more harmful and addictive substances.
Leach is a realist. He said he was laying groundwork for a time when greater acceptance will come - as with other liberal social issues.
"When I first introduced a same-sex marriage bill three years ago, people said: 'Oh, my God, what is he doing?' But that was before the repeal of 'don't ask, don't tell.' It was before President Obama came out for same-sex marriage. . . . Now I don't think someone could win a Democratic primary for statewide office if they didn't support marriage equality."
Leach, of Upper Merion, is seen as one of the most liberal members of the Senate. He easily won a second term in November and is the new Democratic leader on the Judiciary Committee. He is exploring a run for lieutenant governor next year.
In political terms, he has a safe seat. His 11 townships and boroughs in Montgomery and Delaware Counties, including the affluent lower Main Line, all lean Democratic.
This gives him leverage to take a political risk or two. He writes an irreverent personal blog that turns mildly racy at times.
His most recent entry at Daylinsights.com was about the pre-Christmas Pennsylvania Society gathering in New York, where gossip was the prime event. An entry marked "Friday" says: "I woke up fairly early and decided to immediately get some rumors going. As I went for my run, I saw the hotel housekeeper and told her, 'Don't go in my room for a while, you'll wake up Taylor Swift and she hates that.' "
Leach is pushing for new gun-control measures (limiting handgun purchases to one a month and requiring the reporting of a lost or stolen gun). He's also a staunch opponent of school vouchers.
"There is no liberal spokesman in the state right now, and I think he has taken that mantle," said Marcel Groen, the Montgomery County Democratic chairman.
"Daylin's sense of humor is the best I have seen of anybody in politics," Groen said. "Sometimes he gets a little close to the edge. . . . But don't misunderstand the humor for lack of commitment and passion for issues that are important to him."
Leach's Democratic colleagues have entrusted him with a job of utmost importance to them - helping them win Senate seats. They have made him chairman of the Senate Democratic Campaign Committee. Last year, he helped raise $3 million and helped his party gain three Senate seats.
"I know that if you get a reputation for being 'fringe' or 'out there,' that could undermine your effectiveness," he said. "That is why when I take a position that is controversial, I make sure I can defend it."
State Sen. Anthony H. Williams, a Philadelphia Democrat whose district is poorer economically, is an advocate for vouchers and has butted heads with Leach.
He said he respected Leach's defense of public schools. He's a defender, too, he said. But he suggested Leach may not feel the urgency for alternatives to public schools that people feel in badly performing schools. Leach's district, he said, includes some of the best schools in the state.
Similarly, Williams said, Leach might hold a different view on legalizing marijuana if he represented the drug-ravaged communities that Williams does.
Williams painted an image of rowdy youngsters smoking marijuana on rowhouse steps next to an elderly woman trying to enjoy her porch. He agreed with Corbett that marijuana leads to other drug use and community decline.
State Rep. Mark Cohen, a Philadelphia Democrat, has offered bills to legalize medical marijuana - as New Jersey has.
Leach said it may take a one-two punch. Medical marijuana may have to pass first.
He proposes regulating marijuana like liquor - selling it to adults in stores. Colorado and Washington voted to legalize marijuana in November, and he envisions a system one day in which it is sold nationally by brand name.
After Prohibition ended, the violence associated with bootlegging vanished, he said. The same would be true for the crimes associated with marijuana trafficking, he said.
"I believe in taking unpopular positions in politics," he said. "In fact, that's your obligation sometimes."
Contact Tom Infield
at 610-313-8205 or email@example.com, or follow on Twitter @tinfield.