When Jeremy Corbyn was elected leader of the Labour party, many people were in shock. A hard-left member of Labour's awkward squad, a perennial rebel against his own party leadership, and a campaigner for unfashionable leftish causes had been elected overwhelmingly.
He did not look like what a doctor would order for the Labour party. Under the centrist Tony Blair, Labour had won a record-making three elections in a row. Since then the party had moved moderately to the left under Gordon Brown and Ed Miliband. A further lurch to the left looked like electoral suicide.
But, if current polls are to be believed, Labour is now more popular than it was at the last election under Ed Miliband. On current polls, Labour is around 32pc, which is one point higher than 2015.
What of the leader himself. How does the public see Jeremy Corbyn and is the Labour party poll position because of or despite him?
The most useful polling question to look at is to ask the public who would make the best prime minister from the major party leaders. Together MORI and YouGov have been doing this for forty years, so we can look at long-term patterns.
The bar chart shows the support for the Conservative and Labour party leaders ahead of each general election from 1979. (Totals do not add to 100 because of Lib Dems, UKIP and "Don't knows".)
Let's review the history first. The most important fact is that the more popular leader has won the upcoming general election almost every single time. The only exception is 1979 when an under-rated Margaret Thatcher won against the odds. But otherwise, it is essential for a leader to be preferred as Prime Minister.
The second most important fact is that the more a leader is preferred as PM, then the larger is their parliamentary majority. Large leads in the PM-support polls in 1983, 1987 and 2001 translated into three-figure majorities. And smaller leads in the PM-support question in 1992, 2005 and 2010 resulted in more slender majorities. There were two obvious exceptions to this rule. Once was in 1997 when the Blair landslide was not adumbrated by his modest personal lead over John Major. The other, perhaps more significantly, was in 2015 when Cameron's large personal lead over Miliband only resulted in a small parliamentary majority.
Let's see how Jeremey Corbyn is doing. His support levels, at around 21pc, are low but higher than Ed Miliband's. That in itself is quite an achievement for a hard-left candidate for PM. Amongst Labour party supporters, around 70pc prefer Corbyn as Prime Minister, with 25pc unsure. And those are relatively good numbers, since Miliband was only preferred by 60pc of Labour supporters.
The Corbyn magic also reaches particular parts of the electorate that Miliband couldn't get to. Amongst younger voters, Corbyn is actually strongly preferred to May by 52pc to 25pc, whilst Miliband wasn't. (Though the situation is completely reversed amongst the over 65s who split 69-12 for May.) And in Scotland, Corbyn and May are level-pegging within the margin of error. Ironically neither of those groups will generate many votes for Labour since the under-25s don't vote much and Scots are not expected to vote much for Labour.
Let's put all that in its historical context. Jeremy Corbyn also scores better than Michael Foot did with just 15pc support in 1983. But being better than Miliband and Foot is not enough. Corbyn scores less well than the other Labour leaders in the last forty years. In particular, his popularity is less than Neil Kinnock (in 1987 and 1992) and Gordon Brown. And they both went on to lose their elections.
Theresa May on the other hand has reasons to be cheerful. Her popularity as a potential PM is a healthy 42pc. This is higher than all other recent Conservative leaders, except Thatcher. Her lead over Corbyn looks pretty comfortable. Looking at the historical precedents, the current situation most closely resembles 1987 when Thatcher beat Kinnock to win a majority of 102 seats.
The message from the data seems clear. Jeremy Corbyn is doing better than might have been expected. His party's ratings are holding up and he is personally seen as a potential Prime Minister by a significant portion of the electorate. He has energised the base of the Labour party, and has a very strong following amongst younger voters. But if history is any guide, it will not be enough to stop Theresa May and the Conservatives from winning again and probably with a bigger majority.