Could poll maths leave Romney-Biden White House? It sounds like a joke and the chances are slim but America could wake up on Wednesday to the very real prospect of President Mitt Romney and Vice President Joe Biden. As voters across the country head to the ballot boxes on Tuesday, the polls are pointing to an election that is expected to be exceptionally close. That raises the possibility that President Barack Obama and Mr Romney could end up tied with 269 electoral college votes each, one short of the majority required to clinch the White House. In the event of a tie in the electoral college, the House of Representatives, which is expected to remain under Republican control, will choose the president while the Senate, likely to remain under Democratic control, will choose his vice-president. The last time the rule came into play was in 1824 when John Quincy Adams came first in a four-horse race, though he later clinched the presidency when rival Henry Clay handed over his electoral votes. Were it to happen again this week, it would probably make the US's founding fathers cringe. It would also undoubtedly set off a heated debate about what, to many, increasingly looks like an anachronistic way of picking a president. Proponents say the electoral college preserves the rights of smaller states and that without it presidents would focus their campaigns on big states like California and Texas. Critics argue the system is outdated. After all, it was designed at a time when the US had only 13 states and less than 4m people, and no chartered jets or digital media directors to help them traverse the country. To work the system, Mr Obama and Mr Romney have this year focused on nine states accounting for only 110 electoral college votes, with Ohio and its 18 votes the most crucial of the battlegrounds. Many Americans wonder why Iowa, with six votes and 3m people, should warrant so much attention, while Texas, with 38 votes and 26m people, does not. While the possibility of a tie may be alarming but remote, the chance of the electoral college and the popular vote diverging for the second time in four elections is not. National polls show the candidates neck-and-neck, while swing state polls give the president the advantage. This means pundits are bracing for the possibility that Mr Obama will win the electoral college but lose the popular vote. This would be only the fifth time in the US's history that this has happened, but would come relatively soon after the 2000 election. In that election Al Gore, the Democratic candidate, finished with a half-million vote lead in the popular count while George W. Bush ended up with 271 electoral college votes after the intervention of the Supreme Court. Changing the constitution to avoid future divergences is a tall order, but legal activists could look for different ways to make the will of the majority prevail. One way would be for more states to legally require their electors to cast their ballots as directed by the popular vote. Currently 29 states and the District of Columbia do this. Or, as the National Popular Vote campaign advocates, states could pass laws pledging their electoral college votes to the winner of the popular vote nationwide. It has convinced nine states - including California, with 55 votes - to sign on. Others suggest awarding electoral college votes by congressional district, so presidential candidates would be forced to campaign in states currently considered safe for one or other party. For the president's re-election team, these are issues for another day. But losing the popular vote tomorrow would be a heavy blow for Mr Obama: Never before has an incumbent been returned to office without the support of the majority of the people and it could cast doubt on his ability to govern. If Mr Obama is re-elected he will need a clear mandate to have any shot of reaching a deal with Republicans in Congress on looming tax hikes and spending cuts to avoid tipping over the "fiscal cliff." But it could also cast a shadow over the rest of his presidency. Just think of the way some Democrats complained for years that Mr Bush had not been properly elected in 2000. This year the roles could be reversed.