Mike McGinn’s first major policy announcement sank into a political quagmire almost the second he declared his intention to ask voters for $241 million in new property taxes to pay to replace the crumbling seawall keeping Puget Sound from eroding the sand underneath the downtown waterfront.But as he reminded reporters today at a brown bag lunch (to which only shameless alt-weekly types and Joel Connelly bothered to bring actual food), he has other things on his agenda. Most of that, coming up with a plan to replace the 520 floating bridge, expanding bike trails and public transit, making dangerous neighborhoods safer, is still in the seemingly unending discussion stage.