The timing and effect of the earliest human arrivals in North America: "The data obtained show that humans were probably present before, during and immediately after the Last Glacial Maximum (about 26.5–19 thousand years ago) [. . .] We also identify the near-synchronous commencement of Beringian, Clovis and Western Stemmed cultural traditions"

Evidence of human occupation in Mexico around the Last Glacial Maximum: "... we present results of recent excavations at Chiquihuite Cave-a high-altitude site in central-northern Mexico-that [. . .] push back dates for human dispersal to the region possibly as early as 33,000-31,000 years ago."

Evidence grows that peopling of the Americas began more than 20,000 years ago: "... evidence that the initial human settlement of the American continent happened earlier than is widely accepted, and some of this evidence suggests that expansion into the continent began at least 10,000 years earlier than was generally suspected."

A single and early migration for the peopling of the Americas supported by mitochondrial DNA sequence data: "Nucleotide diversity analyses [. . .] suggest that Native Americans and Chukchi originated from a single migration to Beringia, probably from east Central Asia, that occurred [. . .] with 95% confidence intervals between ≈22,000 and ≈55,000 years ago."

Pre-Clovis occupation 14,550 years ago at the Page-Ladson site, Florida, and the peopling of the Americas: "... radiocarbon ages show that ~14,550 calendar years ago, people butchered or scavenged a mastodon next to a pond in a bedrock sinkhole within the Aucilla River. This occupation surface was buried by ~4 m of sediment during the late Pleistocene marine transgression, which also left the site submerged."

Evidence of humans in North America during the Last Glacial Maximum: "n a study of exposed outcrops of Lake Otero in White Sands National Park in New Mexico, Bennett et al. reveal numerous human footprints dating to about 23,000 to 21,000 years ago. These finds indicate the presence of humans in North America for approximately two millennia during the Last Glacial Maximum south of the migratory barrier created by the ice sheets to the north."

And, the Clovis wiki page has good information.

So, there were humans here before the most recent wave of Asians-turned-Native Americans, but about 80% of Native Americans trace their genetics back to the most recent wave... not the waves that were in New Mexico, Florida, Alaska, Brazil and the Yukon much earlier. And the decline of the older groups was sudden, and happened roughly when the two groups first encountered each other. Does this sound familiar?