It's a year this week since businessman Donald Trump shocked the world by winning an unlikely victory in the US presidential election, after a campaign that didn't just rewrite the political rule book, it burned down the library it was stored in.

After a controversial start to his presidency, now we have seen the most significant electoral test of Mr Trump's takeover of the Republican Party and the White House.

Voters in the state of Virginia went to the polls on Tuesday to elect their next governor.

The incumbent, Democrat Terry McAuliffe, was unable to run due to term limits. His Lieutenant Governor Ralph Northam was the favourite to win in a state that Hillary Clinton secured by more than five points over Mr Trump last year.

Northam's Republican opponent Ed Gillespie is a familiar GOP establishment figure. He worked in the George W. Bush administration, chaired the Republican Party, and ran a strong (but ultimately unsuccessful) US Senate campaign in 2014.

After seeing off his more Trump-like rival Corey Stewart in the Republican primary, Mr Gillespie abruptly tacked to the populist right, drumming up fear of immigrants, ethnic crime gangs and wading into other racially charged issues like confederate statues and flags.

Would it prove to be a case of deja vu for Democrats? Would they lose another election they should have won comfortably?

In the end, no.

But they should not be getting carried away thinking this points to a major comeback in next year's mid-terms and an easy reclamation of the White House in 2020.

Democrats have work to do

Pre-election polls showed Mr Northam, who had to see off his own populist primary challenger Tom Perriello from the left, was leading by an average of over three points.

With 99 per cent of the votes counted, Mr Northam won by 53.9 per cent to 45 per cent.

Virginia Lieutenant Governor Ralph Northam, pictured voting with his wife Pam, won the race for governor. ( Reuters: Julia Rendleman )

But given Mr Trump has the lowest approval rating of any first-year president in the best part of a century, and Congressional Republicans have failed to pass any major legislation despite majorities in both houses, this should have been a double-digit walk-over rather than just a couple of points better than Mrs Clinton's 2016 result.

Mr Northam, a centrist, resisted pressure from his party's left wing (led by senators Bernie Sanders and Elizabeth Warren) to speak out more forcefully on issues like protections for undocumented immigrants.

And just as they did last November, those on the left will now argue a more progressive candidate would have generated more grassroots enthusiasm and done much better.

Democrats will try and reassure themselves that they held the middle ground against an opponent who was prepared to play to their populist base, but that was their game plan in 2016 and we saw how that worked for them.

Trump-lite didn't succeed

For Republicans, there are also some unsettling conclusions to be drawn.

Mr Gillespie abandoned his button-down country club persona in favour of a Trump-lite law and order campaign, accusing Mr Northam of sheltering foreign killers and local child molesters. He didn't ask Mr Trump to cross the Potomac to campaign for him, settling for a few tweets and robocalls, but the President cast a long shadow nonetheless.

When the result was known, the President took time out from his trip to the Korean peninsula to chide Gillespie for not "embracing what I stand for".

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Further north, in New Jersey, Republicans lost another gubernatorial election. Republican Governor Chris Christie's popularity in a traditionally Democratic state has long since collapsed into scandal.

Another term-limited incumbent, Mr Christie was once the most popular Republican in the country and a frontrunner for their 2016 presidential nomination, but now represents another failed attempt at middle-ground government.

His lieutenant Kim Guadagna didn't have a chance against Democrat Phil Murphy.

The yawning chasm in the centre

So, a year on from Mr Trump's victory, the shockwaves continue to be felt on both sides of politics.

In the next year, there will be hundreds of House and Senate primaries where the internal tensions of both the Democratic and Republican parties will be on full view.

Both are under mounting pressure to abandon centrism and move to the political fringes.

And while that might inspire the true believers in their respective bases, it widens the divides in Washington. Without the political centre, there is a yawning chasm instead of common ground.

The result, in Virginia in particular, confirms that America's political bridge builders are in danger of going out of business.