The first is tactical - that Ken is in enough trouble on his own side without such unwelcome support which would further exacerbate the suspicions of the right.
But the second is more substantive - that Clarke risks discrediting the liberal vision of a "rehabilitation revolution".
This was the argument made by Sadiq Khan in his speech full text to the Fabians and the Prison Reform Trust tonight.
Khan argued, taking questions after the event, that Clarke's agenda had to be considered as part of that of the government of which he was part - arguing that Theresa May's cuts to police numbers, Michael Gove cutting the EMA, and pressure on education and mental health in prisons, all of which
Hence his argument that:
"It's no use us wanting to cuddle Ken Clarke - I don't want to cuddle Ken Clarke but perhaps others do - when he is part of a government which has got policies which will see the number of people committing crime going up"
That Khan's challenge to the Clarke agenda is reported straight and very fairly by the Daily Mail, perhaps shows just how much they don't like Ken Clarke, with the headline.
We got it wrong 'playing tough so we didn't look soft on crime' says Labour but Clark's gambling with public safety
(Q: How do you get straight and positive Mail coverage of a liberal speech on crime and justice? A: Express it as a a criticism of Ken Clarke).
Pursuing prison reform without resourcing it or getting the implementation right would discredit any progressive reform agenda for a generation, Khan warned.
This was a point which resonated with his liberal audience.
I asked for a show of hands of whether people welcomed the Ken Clarke approach as a positive shift - there was overwhelming support, with only a couple of critics.
But asking whether people felt resources could prove a fundamental flaw in the government's agenda, a large majority agreed. So I asked whether anybody thought the government was aware of this risk, and so likely to make sufficient provision to avoid it: not a single hand for that idea.
Khan was expanding on a point in his lecture, where he offered this critique of the government.
The real test is: do the policies of the Tory-led Government work to bring down crime?
We‟ve seen wholesale cuts to some of the very schemes and initiatives we put in place to help tackle the root causes of crime – Sure Start, EMA, youth provision and unemployment going up, not down. We are also seeing cuts in victims support and also in police numbers.
And on rehabilitation, I‟m unsure the government is offering any real alternative to prison. Prison numbers are being cut not for criminal justice principles but economic principles. As I have argued, a real reduction in crime requires investment in a cross-government approach, not one where a ministers‟ top priority is slashing spending from their own department‟s bottom line, regardless of whether this displaces costs elsewhere across Whitehall.
It‟s clear that the policies of the Ministry of Justice are founded on the short-term need to cut costs, not crime. But in the short-term, successful rehabilitation requires resources.
And successful rehabilitation will not only make society better, it will produce long-term savings – both from the prison budget, and from society as a whole as a result of lower crime.
This government is taking a very short-sighted view on the rehabilitation process
In the long run, they are risking increased costs by gambling with public safety – there is a real and genuine danger that because of their policies crime will rise.
Quite simply, it‟s irresponsible to pursue this agenda without the investment to match it.
Elsewhere, Mary Riddell of the Telegraph is positive about the speech in her column, regarding it as (perhaps) marking "the moment Blairism died", no less.
I am not sure the policy break is as sharp as Riddell sets out, when she argues that Labour was wrong on crime and the causes. In his speech, Khan endorsed "tough on crime, tough on the causes of crime" as a popular and effective approach which helped to cut crime.
Sadiq Khan's Guardian article, previewing the speech, and the Guardian's news report.
Peter Hoskin at the Spectator Coffee House says that a muted endorsement could still undermine Ken Clarke.
David Talbot at Labour Uncut argues that the comparative evidence shows that higher welfare spending reduces reoffending.
Next Left's preview
Ian Dunt previews the speech for politics.co.uk
If you've blogged about the speech and the broader debate, please add a link in the comments. We'll add more links as coverage and reaction appears.