i just saw this and wrote to Patty Murray. I will write to Cantwell too!
Being a National Park, I think it makes sense that cyclists (and others) across the country voice their opinion on this, perhaps to their local representatives as well as to the ones directly involved.
There were major repairs last summer on the road from Nanaimo to Tofino on Vancouver Island (British Columbia, Canada, for those unfamiliar). If you check Google maps you'll see that there aren't really other ways to get from one place to the other than to take Highway 4. It's a very windy, hilly, and somewhat dangereous road, with lots of heavy trucking going on, too. We took that road at the end of August. Lots of parts were on gravel, and there was one-way traffic for significant bits of it, with road workers at both ends stopping traffic for long periods at a time (more than 10 minutes). Nonetheless, I did see cyclists there. Not people on fancy road bikes with skinny tires, but a small number of well-equipped touring cyclists. It would have been silly to go there for a training ride though.
I don't know much about the park and the type of riding that's done there, but I think it it indeed a dangerous precedent to set. People should always have the option of going somewhere without an engine and a few pounds of steel under them.