It's crunch time for the waterfront tunnel, with Mayor Mike McGinn showing his main political skill, learned from years of Sierra Club advocacy, which is to block a project by hammering away at the legal weak spot and putting politicians on the hot seat. And winning over an impressionable media. In the last few weeks, it's been working fairly well.

Add to this another fact of political life. McGinn is starting to look sufficiently weak in public polls that challengers are lining up. Among the names most often mentioned as challengers to McGinn in 2013: City Council members Tim Burgess, Richard Conlin, Sally Clark, and Sally Bagshaw; former councilmember Peter Steinbrueck; State Rep. Reuven Carlyle; and State Sen. Ed Murray. (Don't forget Greg Nickels, either!) The City Council members are pretty firmly committed to the deep-bore tunnel, which gives the others a good opportunity to stake out some popular, statesmanlike positions.

First out of the gate is Ed Murray, pushing for a pro-tunnel, anti-cost-overrun position. Murray would do this by creating an independent board to review Viaduct financing. (That must be the tenth independent board already created.) It differentiates Murray from the supposedly blindfolded tunnel advocates and the obstructionists like McGinn. Another possible compromise: just repair the existing Viaduct and kick the decision down the road for a future governor and the next generation.

Then there is the ever-popular ploy of sending the whole issue to the voters, which has already been tried once (as a way to block the new-viaduct plans of Gov. Gregoire in 2007). The voters would almost certainly reject the deep tunnel, since there are so many groups to dislike it: no midtown exits (angering the people from West Seattle), too car-friendly (stirring up the greens), too expensive (rousing the fiscal conservatives), etc. Even so, referring the issue to the voters is a classic way for nervous politicians to cover their retreat from a hard decision.

Murray is an expert on transportation issues, so he knows what he's talking about. He has also talked about running for mayor for at least the last two cycles, and he almost mounted a write-in campaign after the 2009 primary produced McGinn and Joe Mallahan.

Nothing very remarkable about such politicking, but it's dangerous for the pro-tunnel majority on the council. If a position emerges that allows for more study, more commissions, more consultants, more votes by the public but doesn't seem a transparent ploy to actually kill the tunnel, some councilmembers could defect to this seemingly safe ground. That might prove again McGinn's skill in this kind of oppositional politics — killing something without having the bullet traced to your own gun.