The closer the election gets - and right now the polls have it very tight indeed - the greater the chance that a tie of 269 to 269 will occur.
If a stalemate results, the constitution provides that the vice-president-elect would become acting president until the gridlock is broken.
However, what if the Senate gets tied up in parliamentary knots? It's been known to happen.
Then America is likely to get its first female President, at least until the deadlock is broken. No, she won't be named Hillary Clinton, nor will the acting chief be Sarah Palin. Next-in-line will be the Speaker of the House, Democrat Nancy Pelosi.