You may receive excellent answers here (there are a lot of talented archaeologists hanging out here!), but you may also want to try /r/Askanthropology. Last time I checked, there were still a number of "Clovis First" die-hards, but they are becoming fewer as emerging facts have thinned their ranks. The Idaho discovery is only the most recent in a long list.

While the traditional "solid-ground" avenue produced by melting glaciers may have been used later, it is clear that earlier arrivals traveled along the coast, likely using boats, before the land route was available.