Image caption McAuliffe and Cuccinelli have gone head to head in debates

Voters in the US state of Virginia go to the polls on Tuesday for a new governor. So why does it matter to anyone else?

Only one in three people voted when Republican Bob McDonnell became Virginia's 71st governor in 2009. That's fewer than two million people.

So the contest to become his successor might not seem like a battle of national, even international, importance.

But the result of Tuesday's election - between Democrat Terry McAuliffe and Republican Ken Cuccinelli - will have implications far beyond the Blue Ridge Mountains and Chesapeake Bay.

It's a key swing state, closely contested in presidential elections, but it's a different electorate who make the effort to vote in these kinds of elections. In fact, for 36 years, whichever political party holds the White House has lost the governor's seat a year later.

There's a theory that presidential candidates are at an advantage when campaigning in a state with a friendly governor, but it didn't help Mitt Romney win the state in 2012. So why is this election important?

1. It could shape Republican identity

In Virginia, the Republicans have put forward a candidate closely allied to the Tea Party, the group that other members of the party have blamed for the recent government shutdown.

National Republicans should be really worried if McAuliffe wins, says Craig Brians, professor of political science at Virginia Tech.

"They could be thinking: 'This is perhaps the second time in a month that people associated with the Tea Party have really hurt us and we need to rethink things.'

"At some point, the national Republican party needs to decide: 'Are we going to be a majority party or go to the right, stake out that ground and maybe never hold national office again.'"

The emergence of a third-party candidate polling at double-figures, libertarian Robert Sarvis, reflects the fissures within the Republican party, says John Avlon, author of Wingnuts: How the Lunatic Fringe is Hijacking America. Libertarians traditionally vote Republican, he says, but many have been put off by Cuccinelli's extreme social conservatism.

2. There's a Hillary factor

Both Clintons have helped McAuliffe, who was co-chairman of the former president's re-election campaign and chairman of his wife's 2008 presidential campaign.

"Terry McAuliffe is a really old friend of Bill and Hillary Clinton so the fact that they would come and help him campaign is not surprising. But they are not super popular in Virginia so the fact he brought them here is interesting, in the sense that Hillary is keeping her hand in, simply by being part of it and keeping her face in it," says Brians.

With Hillary braced to run in 2016, a McAuliffe win would be interpreted as a boost for her, he adds, because such a divisive figure inflicted no fundamental damage to his campaign.

Writing in the National Review, conservative blogger Jim Geraghty goes even further and suggests it's been a dry run for the Hillary campaign machine.

3. It's what the US is going to look like

Where they stand Cuccinelli: Pro: Income tax and business tax cuts, abortion restrictions, gun rights

Income tax and business tax cuts, abortion restrictions, gun rights Anti: Obamacare, gay marriage McAuliffe: Pro: Expanding clean energy, gay marriage, some business tax cuts, Obamacare, stronger gun laws

Expanding clean energy, gay marriage, some business tax cuts, Obamacare, stronger gun laws Anti: Tightening abortion laws

The demographics in Virginia are changing in the same way as they are across the country - a growing Hispanic and Asian population, and more people in urban areas.

"It's a microcosm of what's happening nationally," says Dustin Cable of the Weldon Cooper Center for Public Service, especially in southern cities like Atlanta and Raleigh.

The northern Virginia suburbs are a Mecca for young college-educated professionals, he says, many of them federal employees working in Washington DC.

These groups have helped Obama win two elections but it's not yet clear how these shifts will play out in elections that historically have older, white voters, says Cable.

4. Effects on Obamacare

Supporters and opponents of the highly controversial Affordable Care Act, Obama's signature law that aims to extend health insurance coverage, will be watching Virginia.

Cuccinelli has led the battle against Obamacare in the state, says Brians. If he fails, people could infer that voters in Virginia are in favour of Obamacare.

The present governor, Republican Bob McDonnell, has said no to expanding Medicaid and no to running a state insurance exchange. McAuliffe has said he will reverse both those if he wins.

"That will make a huge difference in one of the biggest issues of the campaign," says Brians.

5. It's provided comedy fodder

When Ken Cuccinelli proposed outlawing sodomy and oral sex, he immediately earned national coverage on The View and The Daily Show, as the likes of Whoopi Goldberg and Jon Stewart ripped into him.

His opponent, Terry McAuliffe, was not spared either. At a debate, he was asked by the Daily Show if he thought his image had improved from debilitating to moderate revulsion.

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