After months and months at the top of the polls, there is a real possibility that Donald Trump could be the nominee.

[Donald] Trump has said he will accept the results of the election - if he wins. And he has said the only way he can lose the election is if it's stolen from him. Weeks before any votes were cast, he was predicting widespread voter fraud. So if he loses, what does he do?

Michael Rubio said Trump's plan was impulsive and not well thought out. The other thing that's really annoying Republicans is that this was supposed to be their great week. The president gave a speech on terrorism that was not well received. They were working hard to tie Hillary Clinton to the president. Then along comes Donald Trump, and the story changes dramatically.

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.

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.

As one person said to me , Republicans know [Donald] Trump is a stain on their party.

If Pat Toomey of Pennsylvania wins, for instance, it will tell Republicans that their own brand hasn't been hurt too badly by [Donald] Trump's negatives.