Between his sway with rock stars, appeal to the kids, and now the sole endorsement from the Sierra Club, it might appear Dow Constantine is becoming the most likely Democrat to make it through the August King County Executive primary. Technically it’s non-partisan but conventional wisdom says the Republican-leaning Susan Hutchison will take the conservative vote and pick up enough on name recognition to win the primary. That leaves the four Democrats to split the rest (with a handful going to long-shot candidates). And Dow’s been hitting a few apparent home runs, including today’s Sierra Club endorsement. “Dow Constantine is a steadfast and proven leader for protecting our cherished natural environment,” Sierra Club political chair Scott Otterson says in a press release. “Dow not only has the strongest record, he has a clear vision for the future, including promoting clean technology jobs, investing in transit solutions and immediate action on climate change.”But none of this means Constantine can sit on his laurels. While he’s been aces with the groups one typically associates with the far left, Larry Phillips has been locking down union endorsements. Unions and old people (those grandmas in Ballard who have been voting Phillips into his county seat for years) are more likely to actually vote in an off-year primary election. Constantine needs to remember that getting support is hardly a guarantee of getting ballots.The candidates are debating again tonight (with another rare appearance by Hutchison) in North Bend. Twin Falls Middle School, 46910 SE Middle Fork Rd, at 7 p.m. if you’re interested.