This is a handy tool from fivethirtyeight to assess the effect of incremental movement in certain swing groups.
http://projects.fivethirtyeight.com/...-the-election/
I have played with it a little, and it hammers home the point for me that the GOP really needs to make inroads among certain key demographics (such as Latinos) in order to have a hope of winning the electoral college this fall.
It also shows Trump's main weakness: his key demographic is non-college educated white voters. Even if turnout in that group goes through the roof, and Trump significantly increases his vote share, he can't win with them this fall. This is a group that is actually pretty powerful in an electoral-college sense (Pennsylvania and Ohio) are two key swing states that could be affected, but this won't offset the fact that he will lose Latinos, African-Americans, and may lose part of the GOP's traditional slight advantage among college-educated white voters, a group he hasn't done especially well with.