As their economy nosedived into depression, President Franklin Roosevelt famously told the American public that there was nothing to fear except fear itself.

Fear was the enemy of the good.  Hope was the friend of recovery.  And from that it has generally been held that the combination of change allied to plausible hope is the winning ticket in any political contest.

But here we are, with less than a month to go in the EU referendum, and we are still mired in the depths of Project Fear.

Why so?  Because it looks like it may be the only approach that’s going to work.

In itself, it isn’t popular.  The commentators sneer at it, and the voters are complaining about it, responding with the seemingly endless refrain, ‘just give us the facts.’

Really?  So the campaigns are supposed to send everyone sets of trade tables, and EU accounts sheets, and sets of migration statistics?  That would be novel.

No, Project Fear has a place here – sad though it is to admit it.  It will probably work because of the political dimensions of this choice.

On the one hand, there are millions of committed anti-EU voters.  All ready to vote Out and impervious to any further argument.  On the other hand, millions (although fewer) committed to the UK’s EU membership and equally impervious.  If these two groups went head to head, Out would most probably win.

The outcome rests with those not in either of these groups.  These comprise the undecided, who will vote whichever way they finally opt for, and the unmotivated, who might just not bother in the end.  Remains task is to bring the majority of these folk to their cause.  So it’s a double-headed task: pull the undecided across, and motivate the unmotivated.

That’s not easy.  Remain are not campaigning for change, but for status quo.  It’s hard, if not impossible, to get people enthused about that.  Remain simply do not have the advantage of the ‘change’ message.

Nor is winning a referendum like winning a general election.  This isn’t about a mandate for government, or the election of senior public office holders.  There is an issue at stake, not a government.

The winning combination in politics is change plus plausible hope.  For remain, change is out.  So what about the plausible hope part of the equation?  That would require setting out a vison of an alluring future in the EU.  A Europe of reform, delivery and progress.  See the problem?  That is never going to ring true, with the EU as it is today, struggling with faltering economies, a migration crisis, and resurgent nationalism.

So instead of change and plausible hope, what do you do?  You have little option but to portray your opponent’s pitch as a dangerous change with ‘hope’ that is only implausible.

So you have to talk about risk.  And risk invokes fear.

Project Fear is a tough challenge for the Leave side.  Remain produces a string of reports sketching out the dire consequences of Brexit.  Lots of numbers included, and lots of endorsements from those outside the political mainstream.

What can the Leave side do about all that?  The best option is to produce equally weighty counter-reports, also backed up by prominent figures outside the political mainstream.  It isn’t happening.  So instead the only option is to rubbish the reports and the endorsers.  So the regularly repeated message is that all these organisations got everything wrong in the past, and that people like the Governor of the Bank of England should shut up.  And that message does not play at all well with voters wanting ‘the facts’.

So Project Fear seems to be wrong-footing the Leave side.  They feel that their strongest card is immigration.  And how are they playing that?  With their own project fear, fuelled by talk of a seemingly unstoppable onslaught of immigration far into the future.  And if you are playing project fear with your own trump card, can you credibly denounce the other side for playing project fear with theirs?

To get the undecided and the unmotivated voting for Remain does not require their endorsement of a bright EU future.  They cannot be persuaded to vote for a cause that isn’t much liked.  Instead they have to be motivated against something they would rather avoid.  It’s a case of ‘why take the risk, if we don’t have to?’

Project Fear will run until June 23.  The resentment of it could play out later.