The Tampa Port Authority's decision to withhold a subsidy from the downtown streetcar until the trolley system comes up with a stronger business plan could be a helpful turning point for this key public asset. The port should use this leverage, though, to make the trolley much more integral to the remaking of the Channel District.The board's move Tuesday should stir the creative juices in the nonprofit trolley operator's fundraising efforts and help bring the trolley into the mix as the city, the port and Tampa Bay Lightning owner Jeff Vinik work on a master plan to develop Vinik's Channelside shopping complex and 24 acres he owns near the hockey team's home at the Amalie Arena.The streetcar is not dependent on the subsidy; a far bigger drain is the $426,000 the trolley pays for insurance every year to cross the CSX tracks in Ybor City. But the subsidy helps the bottom line for the struggling operation and serves to remind the port that the streetcar plays a vital role in supporting the port's presence in the Channel District.The streetcar is exploring new revenue streams, and officials are considering extending service deeper into the downtown core, where it could attract a broader mix of paying customers. These are promising strategies that could stabilize the trolley and position it to grow. The port is a major player along the waterfront, and it should recognize the trolley as a critical transportation link for this fast-growing, mixed-use community. The trolley, in turn, needs to meet its potential of bringing real value to downtown.