It's probably important to remember that the ancestry of native Americans may be complicated. It's possible that pre-Clovis culture traveled down the coast, then radiated from there, and then some time later, Clovis culture traveled the inland corridor route, and then these people - already distantly related, anyway - intermingled. So I'm not trying to say that there was only one founding event; there may have been several. But I do think the common understanding now is that the people associated with Clovis interbred with the pre-Clovis people, rather than replaced them outright. And, again, both the pre-Clovis and Clovis people were probably descended from the same stock of Siberian peoples who settled in Beringia ~20K years ago.