Senate races have tightened along with the presidential race. Watch to see how many Republican Senate candidates outperform Donald Trump - and how many hang on to their seats in states that he loses.

Until he announced his immigration policy last week, Obama had the support of most Hispanic voters - but not the enthusiasm they had shown for him in 2008. That may be changing in part because of the decision not to deport young immigrants whose undocumented parents brought them here as children.

As those states and others in the South and West become more diverse and educated, they will become harder for the Republican Party - in its current form - to win.

If [Donald] Trump drags down a bunch of Senate Republicans, the post-election GOP assessment will be much more pessimistic.

If [Hillary] Clinton can come close in those two traditionally red states, it will be because of the diverse, educated populations around Atlanta and Phoenix. And it will be a sign that Arizona and Georgia are on their way to becoming the new battleground states.

Romney still enjoys the Republicans' traditional advantage among voters who are veterans, but the Obama campaign is confident it can chip away at that.

If [Hillary] Clinton wins, history will also be made: She would be the first female U.S. president, of course, but also the only candidate in the modern era, other than George H.W. Bush, who managed to follow a two-term president of her own party.