Cameron would prefer not to share power with Ukip. What matters is the price at which he could bring himself to do it in an emergency. Does he distance himself from Farage out of rhetorical expediency or because he finds the man and his party fundamentally objectionable? Is there a line of anti-European, anti-immigrant rhetoric he won’t cross?
The answer to those questions – and how a majority of Tory MPs might answer them – will tell undecided voters a lot about the character of the party and its leader. And the question will get harder to avoid. The Tories have been eager to argue that supporting Ukip could accidentally ease Miliband’s path to power, in the belief that such a prospect will send dissident Conservative voters scurrying home to Cameron’s camp. But the proposition can just as easily be reversed as a warning to anyone who thinks Ukip rhetoric is beyond the pale but is tempted to back the Tories. Vote Cameron, Get Farage? The prime minister used to rule it out. It is revealing that he no longer can.