Prime Minister Boris Johnson's Conservative party won a historic victory in Thursday's U.K. general elections. Based on the exit polling, the Tories are on track to win 364 seats, far more than the 203 seats Labour is predicted to win, and well north of the number needed to govern. Johnson's campaign has been as decisively vindicated as could realistically have been imagined.

Just how historic was this win? Let's examine.

First of all, it is by far the strongest outright majority for any party since Tony Blair left the premiership — indeed, larger than Blair's own last victory in 2005. In that race against the Conservatives' Michael Howard and Charles Kennedy's Liberal Democrats, Blair won 35.2 percent of the vote and 355 seats — a dramatic decline from his previous victory, and well shy of Johnson's result, both in seats and especially in terms of the popular vote.

Since then, Britain has had three elections without a decisive result: In 2010, David Cameron's Conservatives won a plurality of 306 seats with just over 36 percent of the vote, and had to govern in coalition with Nick Clegg's Liberal Democrats; in 2015, Cameron was able to squeak out a bare majority of only 330 seats with just shy of 37 percent of the vote; and in 2017, of course, Theresa May, having inherited the premiership from Cameron, gambled on an early election to increase her majority, and instead lost it, winning only 317 seats, only tenuously holding power with the support of the Democratic Unionist party from Northern Ireland.

Johnson, with this victory, has blown the logjam to smithereens. But that understates the historic nature of his triumph.

The Conservatives have already faced the electorate twice since Cameron's victory in 2010. It is distinctly rare for a party to win a fourth mandate to govern. The last time it happened was in 1992, when John Major, who had taken over as prime minister from Margaret Thatcher, won his first mandate with 336 seats (a decline of 40) and just under 42 percent of the vote. Since World War II, no party has won a fourth mandate with an increase in seats, and the last time either party changed prime ministers and then won an expanded majority was with Harold Macmillan in 1959.

Moreover, and this is the historic comparison that Johnson would probably best prefer, his is a larger majority for a new Conservative government than Thatcher's breakthrough in 1979. (Blair won a much larger majority of 418 seats in his first outing in 1997, albeit with only a bit over 43 percent of the popular vote.) The Iron Lady won 339 seats with just shy of 44 percent of the vote, and transformed British politics for a generation.

Johnson's transformation of the Conservatives is what most merits the Thatcher comparison. He is the first Conservative leader to campaign on leaving the EU, and before the election he purged the party of dissenters. Now, with a solid majority in Parliament who owe their seats to his electoral strategy, Johnson is in a position to deliver on the central promise of his campaign and get Brexit done.

What then?

The details of exiting the EU will inevitably be devilish, but Johnson is already in a strong position to bulldoze one obstacle that stymied May's own negotiated Brexit deal. May's minority government needed the approval of the DUP, and they refused to accept any agreement that distinguished Northern Ireland from the rest of Britain in terms of customs. But there is no way Britain could leave the EU and preserve a customs-free border with the Irish Republic without making precisely such a distinction. Johnson's Brexit deal cut the Gordian Knot (though he has not always been forthright in admitting it), and he is now in a position to deliver even if the Queen's subjects in Ulster object.

But Johnson's real challenge lies not across the Irish Sea but over Hadrian's Wall.

Apart from Johnson's large majority, the most dramatic story of the night was the overwhelming victory for the Scottish National Party, projected at 48 seats. To make clear just how overwhelming that victory is, Scotland only has 59 seats in Westminster. And while the SNP did even better in 2015, the context has shifted considerably in the wake of the Brexit vote. Scotland voted by a margin of 62 percent to 38 percent to remain in the EU in 2016, but were outvoted by their far more numerous English neighbors. In 2017, the first post-Brexit election, the SNP dropped 21 seats and a third of their vote, but now have come roaring back. Against the backdrop of Johnson's pro-Brexit campaign, the message could not be clearer about Scots' limited confidence in a future within the U.K.

Johnson won in large part by combining a commitment to restoring British sovereignty that animated the most passionate Brexit voters with a reassuring message about continuity and protecting British institutions. He did not run an anti-immigrant or "little England" campaign, and he ran explicitly against the austerity economics of the Cameron years. His greatest challenge post-Brexit will be to turn to the other side of that same coin, convincing Scottish voters that both their sovereignty and their social values are adequately expressed within the United Kingdom, and will remain so under his Tory government.

If he can do that successfully, he will truly have earned his place in history.

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