IBD/TIPP National: Clinton 45 Trump 40

[Mr. Morden]

On page 49, it says 595 white voters and 169 Black/Hisp (764 together). So they have a 78% white sample??? Not sure why it doesn't add up to their total of 828.

No.  78% of the people responding doesn't mean that they're assuming a 78% white electorate.  It just means that 78% of the people who responded to their poll are white.  But every pollster does demographic weighting once they've conducted the poll.

[Mr. Morden]

I didn't see them as a subgroup, but I guess if you divide the white # / total #, it's 72%, instead of dividing white / (white+black+hispanic)...

Right.  But again, that's just the %age who responded.  They presumably did some weighting (like every other pollster does), so we don't actually know what is the inferred racial breakdown once weighting is applied.