London (CNN) On December 12, the UK will finally have a general election . In all honesty, it's needed one since June 9, 2017.

That was the morning Theresa May learned her gamble to hold a snap general election had backfired. May's plan was to increase her tiny majority in Parliament to over 100 seats. Instead, she lost the small upper hand she had which made the delivery of any kind of Brexit impossible.

Boris Johnson is learning this the hard way. Having inherited May's minority government, Johnson discovered early on that his optimism wasn't enough to get Brexit done.

Despite doing the seemingly impossible and getting a new deal from the EU, he simply doesn't have the numbers in Parliament to pass the legislation required to deliver Brexit. Holding an election in which he secures a fresh majority was his only real option.

It's a gamble. Having promised to exit the EU by the end of October, Johnson risks not only further delays, but the prospect of losing Brexit altogether. Though he enjoys healthy poll leads right now, a lot can happen during an election campaign.

"A 15% lead sounds a lot, but voters can come back home or change their mind," explains Will Jennings, a Professor of Political Science and Public Policy at the University of Southampton. "The thing to note with Johnson is he doesn't start even with the level of support Theresa May had in 2017."

Johnson's first big problem is the main opposition Labour Party. As May discovered, Jeremy Corbyn, Labour's leader, is a very effective campaigner. Corbyn surprised everyone in 2017 by picking up far more seats than expected. He did this despite being an underdog and with May looking like a strong, popular leader who had a plan to deliver Brexit and get on with an ambitious domestic agenda.

This time around, his job is arguably far easier. Johnson's aggressive political strategy since taking office has allowed Corbyn to paint himself as the anti-Johnson. Corbyn is making a lot of noise about the fact that Johnson is on friendly terms with the President Donald Trump, a man who is very unpopular with the British public.

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Corbyn says that Johnson's myopic obsession with securing a trade deal with America would mean selling out the UK's National Health Service (NHS) to US drug companies. And Trump handed Corbyn a priceless soundbite earlier this week, when he called the London-based talk radio station LBC to heap praise on Johnson and say that the opposition leader would take the UK "into such bad places."

The NHS is the closest thing that the UK has to a religion and it will no doubt feature heavily in this election. And as Jennings points out, this could prove tricky for Johnson's Conservatives "if they end up getting sucked into winter NHS crisis" in the middle of a campaign.

Also in Corbyn's favour this time is the fact that he has a very clear path to office, something no one believed could happen in 2017.

If the UK ends up with another hung parliament and Corbyn is the most successful loser, he could credibly make the case he should head some kind of coalition or minority government. The price for doing so would almost certainly be a commitment to some kind of second Brexit referendum.

This would be terrible for the Conservative party. Right now, the party is reluctantly united around Johnson and his Brexit deal. However, if another referendum were to happen, the party would tie itself in knots over exactly what position to back.

Losing Brexit isn't the only thing spooking Conservatives. Corbyn is, in the eyes of Conservatives, a danger to the nation. They believe he is a threat to national security and that his hard-left agenda would wreck prosperity. In the words of a senior government advisor, "people need to know that Corbyn will take their houses, nationalise their jobs and tax them to death. It should terrify anyone involved in this election. There is a real chance that Corbyn could end up in Downing Street."

A Labour spokesperson refuted this, telling CNN that "Labour will put wealth and power in the hands of the many. Boris Johnson's Conservatives, who think they're born to rule, will only look after the privileged few."

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Conservatives also fear that Corbyn's dream of stepping inside Downing Street would come at the cost of getting Scottish nationalists on his side. And the price for this would be giving Scotland another Independence referendum. After three years of Brexit chaos, many Scots now believe that the best path is to go independent and rejoin the EU as a full member state. Experts are split on exactly how that vote would go, but for a party formally known as the Conservative and Unionist Party, it's a terrifying prospect that would forever be blamed on Johnson's administration.

Conservative aides are privately concerned that Johnson has not learned the lessons of 2017 and are worried that his hubris will come to bite them. Talking to senior staffers, their most optimistic predictions are that Johnson will win a small majority and get his Brexit deal through Parliament, only for the party to fall apart over the UK's future relationship with Europe. They point out that even if the deal passes, the UK only has 11 months to get the rest of Brexit sorted. And that will result in extending the transition period.

They are also well aware of the real prospect that the election will result in another hung parliament. That effectively kills the Johnson government, something which has not gone unnoticed in Brussels. EU officials are pleased that an election is happening, hoping that it will finally provide some answers to this seemingly impossible question. But they also think that a hung Parliament is the most likely outcome. "To be honest, there is already chatter about the next extension," an EU official told CNN.

If that happens, the deadlock continues. "If there's no majority then there's a question of whether he (Johnson) resigns. I am not even sure we get to a second referendum ... before we even get there we could be looking at a February election," says Professor Will Jennings.

Johnson's Brexit gamble was a table-flip moment. It's the last option for a Prime Minister who's been on the back foot since day one. But in flipping that table over, he could soon discover that there was far more on it than Brexit. Johnson might live to regret wanting to have a crack at this leadership business.