A last-minute Sonoma County political battle has erupted over extending the quarter-cent SMART sales tax for another 30 years. Marin voters are along for the ride.

Molly Flater, the daughter of a Sonoma County developer, and Graton Rancheria, the tribe that runs the Rohnert Park Indian casino, are the big investors in this battle.

Flater has contributed $850,000 to fight Measure I, questioning the public costs and benefits of the commuter rail line and the way it is being run.

The tribe says its $1 million pledge is part of its commitment to the green “benefits” of having the Sonoma-Marin Area Rail Transit system as an alternative to commuting by car and to quell the show of political clout by a well-heeled family.

SMART, launched by voters’ passage of 2008’s Measure Q, has been up and running for just over two years. That’s not very long to judge the long-term performance of a new transit service, especially one that is still miles from completion promised in Measure Q.

It’s also not a very long track record on which to ask for a 30-year extension of a tax that Measure Q put in place until 2029.

SMART says extending the tax to 2059 would put it in a fiscal position to refinance its bonds and save an estimated $12 million per year. The extension would give it more leverage for state and federal grants, which SMART has already proven effective in garnering.

The SMART tax — just a quarter-cent on every dollar in taxable purchases — is a small price to pay. But winning passage of Measure I, which needs a two-thirds supermajority vote, is dicey.

Regardless of the campaign warchests, SMART already has its critics, ranging from those who don’t like hearing train horns to those who complain that it is neither affordable nor convenient. There are complaints that SMART creates more traffic congestion on city streets while doing little to relieve gridlock on Highway 101. In addition, some local bike advocates complain that SMART has been too slow in keeping its promise to build a 70-mile bike path running parallel to the train tracks.

But SMART is a promising a multi-modal alternative to getting up and down the Highway 101 corridor. Its ridership — now about 2,500 daily weekday riders — is slowly growing, particularly with its recent extension to Larkspur Landing and the ferry terminal. As SMART grows northward, to Windsor and Healdsburg, its ridership should rise.

Local employers, many who help subsidize workers’ fares, understand cost in time and cash of making the 101 commute by car is a significant hurdle in recruiting and retaining employees.

SMART, in its start, has had some stumbles. While performing a remarkable feat of building and launching a new rail system, SMART also is expensive and that remains an obstacle for building ridership across all income levels and ages.

The recent dustup over SMART not releasing detailed ridership figures could have been avoided by a greater level of board members’ oversight. It took multiple tries to win voter approval of Measure Q. It might take a second try to win its extension. It is just too soon in the agency’s track record to extend its tax to 2059.

SMART will need a longer-term investment. The IJ endorsed SMART in 2008. We continue to support the promise of inter- and intra-county train service.

A high-priced political war among Sonoma County titans may likely spell the fate of Measure I.

While the IJ editorial board continues to support the vision and promise of SMART, it is too soon to be be asking for such a lengthy extension. Far from mothballing its fleet of trains, SMART needs to build its ridership and return to the ballot in — possibly — 2022, providing voters with two more years of progress on which to base their decision.