Boys, Boys, Boys don't shoot the messenger just pointing out facts for reality.
The shifting ethnic demo and the growth of minority population is a result of two factors (1) immigration, (2) higher birth rates.
Trump obviously has no control over the later but the first is without question a focus of him and his administration. Everything from reducing and changing immigration quotas, building a wall, limiting or elimination political asylum, to an outright attacking on the 14th amendment.
These efforts will have little or no effects on this year elections for a couple of reason. The first three because any effect on the actual voting base is a decade long process as immigrates can not become citizens for a minimum of five years so anyone Trump has prevented from entering the U.S in his time in office would not be a voter anyway. If anything he incentivized previous immigrate to become citizens to protect their status. Secondly despite his hatred of it the 14th amendment is part of the U.S. constitution and he can't do anything about it.