I'm not sure what "political leanings" on the Camas Prairie or anywhere else in Idaho would make the CSP right of way any less likely to become a trail than the ones in Kootenai, Benewah, and Shoshone counties. Most of the Route of the Hiawatha trail lies in Idaho. There's the 72-mile all-paved Trail of the Coeur d'Alenes (ex-UP and some NP) between Plummer and Mullan, plus the un-paved portion of the NP over Lookout Pass. Several miles of ex-UP (much of it paved)from Coeur d'Alene northwest to Feeley Spur. Alternating segments of ex-GN and MILW trail, all paved, from Post Falls west to the WA/ID line. Ex-UP trail segments in Sandpoint. Moscow west across the border to Pullman. I could keep going.

Now, I could see issues of adjacent land ownership and social perceptions hindering a CSP trail. Route of the Hiawatha was almost entirely in Forest Service territory, so it had little local resistance and plenty of federal support. Trail of the CdA's had substantial opposition from adjacent land owners, but their fears of people camping and trashing and trespassing have been proven wrong. Some Camas Prairie ranch and farm owners will probably have similar concerns, whether unfounded or not.

Reasonable access from I-90 and proximity to population centers like Kootenai County and Spokane have helped make the Route of the Hiawatha and Trail of the CdA's hugely successful. The west end of the Trail of the CdAs is actually accessed from U.S. 95, the same highway that would be the main access to a trail up Lapwai Canyon and across the Camas Prairie. But as said earlier, there's not a huge population center down there other than Lewiston/Clarkston. Summer tourism makes that stetch of U.S. 95 a busy place, but I'm not sure how many folks would drive all the way there from Spokane/CdA or Boise just to bike a trail. Hardcore trail bikers, yes, but the average family looking for a fun day out with the kids, not so likely.