So as to better cover the Lib Dem leadership race and hence improve the information available to party members ahead of a key decision, I'm staying neutral in the contest. But the following is, for the reasons set out, crucial to deciding who to vote for - whichever candidate you are leaning towards.
P.S. There is still time for party members to take part in my leadership election survey.
Vince Cable's approach to working with other parties
During his time as Liberal Democrat leader, Vince Cable had a triple-track approach to working with those who share (some of the) party's values but are not in the Liberal Democrats.
One track was party reform, with the introduction of a registered supporters scheme as a way of making it easier and more effective for the party to work with those for whom full membership is a step too far for them.
The second track was making very positive public noises about those who might leave other parties - hence his warm words about those who initially formed The Independent Group and an openness to working with other parties ahead of the European elections, even though that came to nowt.
The final track was an encouraging attitude towards any local parties who wanted to do deals with other parties. He didn't use the powers of a party leader to try to discourage or even hinder such arrangements, and indeed championed a local deal with the Greens in the London Borough of Richmond. A slow spread of grassroots election pacts took place during his time as leader.
The options for the next Lib Dem leader
For the next Liberal Democrat leader, continuing this sort of approach is definitely an option - continuing to change how the party works to better engage with those outside the ranks of formal members and seeking to encourage in a relatively hands-off way more arrangements with other parties.
But under the next leader, the party has two alternatives: to do more, or to do less.
Work more closely with others?
Do more, as in going beyond welcoming a spread of local deals by instead actively seeking out more of them. That could be particularly attractive if there is a general election triggered later this year by a Brexit crisis - making deals to ensure there is a (fairly) united Remain ticket in the election rather than risk splitting the Remain vote under first past the post.
What's more, if the idea of uniting the Remain vote behind a cross-party mix of candidates in different seats is taken as a serious runner, the best way to do this requires some specific administrative work to be prepared.
As I wrote before about how to create a pro-European umbrella operation, the way to do this is:
… to make use of a detail in election law created to help the Co-operative Party.
This allows a candidate to stand as the joint candidate of two different political parties, with the news that they are a joint candidate reproduced on the ballot paper.
That ballot paper point is crucial because it means that right at the point of voting, people know exactly which candidates have the backing of parties. No messing around with hoping people will look up preferred candidates on a tactical voting website. Instead you get the message right in front of every single voter at the point at which they vote.
Yet by backing candidates of existing parties you also get the benefits of their existing organisations and voter loyalty.
So, you create a new pro-European political party, but rather than try to make it in a fully functioning traditional party, you instead make it an umbrella coalition. Offer any candidate of any party the chance to get an official endorsement from the new party if they agree to a certain number of basic principles (European policy most obviously). If a candidate signs up, give them the right to use the logo and name on the ballot paper.
This idea of group acting as minor political party in order to win coverage on the ballot paper and hence increase its electoral leverage - both to get candidates to agree to its policies and then to win votes for those candidates who do - is something aficionados of American politics may recognise. It is what US political parties such as the Working Families Party do, with a few wrinkles due to the different electoral law their but the same underlying purpose and method.
To do that requires a deliberate choice by the Liberal Democrats centrally, going well beyond the benign oversight of the spread of a few local deals.
Or work less closely with others?
But instead, under the next leader, the Liberal Democrats could instead do rather less in the way of cooperating with those outside the party.
Flush from the local election success, the Euro elections triumph, the failure of other would-be new parties and another surge in membership, the party could take a much more bullish line: the Lib Dems are the effective, growing Remain choice, so if you want Remain vote for us and join us. No deals or pacts required.
The choice for party members
That choice - to double-down on cooperation or to double-down on focusing on the party - is one which the Lib Dem leadership contest offers. Although at times the rhetoric of Jo Swinson and Ed Davey get rather close on this topic, the overall tone and direction of their views are clearly different. Swinson is the one keenest on maximising cooperation with others, Davey the one keenest on minimising it with a focus on the party itself instead.
Curiously, neither seems to want to make as much of this difference as they could. Even though many party members are struggling to see that much of a difference between the two, neither is using it as an issue - so far at least - which to clearly say 'what you'll get with me is different from what you'll get with them'. Jo Swinson, for example, at most refers to this difference only obliquely in her vision. Ed Davey even told Mumsnet that. "I've not noticed any difference between Jo and me on this".
Perhaps both think they are the frontrunner and want to play safe. Perhaps both think the party is too divided on the issue for taking a clear stance to be a winner. Perhaps both have been too busy to really crystalise in their own minds their strategy for the party.
Whatever the explanation, there is a substantive difference between them, and it's one we've seen for a fair while now, including going back to pre-Christmas and how much keener Jo Swinson was on creating a registered supporters scheme than Ed Davey. She promoted the idea in advance of the conference debate and then spoke in it, for example, whilst he did neither.
Or in the last few days with their contrasting media comments:
Jo Swinson has said if she was leader of the Liberal Democrats the party would work with other parties and put up joint candidates that support a second referendum…
By contrast her rival Ed Davey appeared to dismiss the idea by saying: "Anyone on our side who suggests a pact would be selling the Liberal Democrats short. A pact would simply blunt our clear anti-Brexit, pro-environment message." [The New European]
That reflects the differences that have also come through clearly when I've spoken with them over the last year. I'm sure each could serve happily under the other, but it will be a different approach the party takes depending on who is leader.
Exactly how those different approaches would play out under a Davey or Swinson leadership depends to a significant extent on wider circumstances, such as the level of interest from other parties or the defection choices of other MPs.
Yet each would head off into that uncertain terrain with rather different priorities, instincts and preferences.
That makes the choice between them in the leadership election a crucial one, especially as this is one area where it is hardest for party members to subsequently influence what a leader does through conference votes and the like. Not impossible, but harder than other areas. The up-front choice of who is going to be leader is more consequential than it is for the party's policy, for example.
That's why this issue of how to work with those who share (some of) the party's values but are not in the party should be a defining one for members choosing who to back as party leader.
The 2019 Lib Dem leadership election is being covered by me both in podcast form with Stephen Tall in Never Mind The Bar Charts (subscribe here) and in email newsletter form with Liberal Democrat Newswire (sign up here).