A Labour Party that goes into the looming general election campaigning for a new Brexit referendum, which Jeremy Corbyn says it will do, will delight Boris Johnson and fill EU leaders with despair.
Because Johnson will think millions of British people will recoil at the idea of a general election followed by referendum in quick succession.
And Johnson will also be delighted that he would face a warring opposition, since LibDems, Greens, SNP and Plaid Cymru are clear the UK must stay in the EU whereas Corbyn’s Labour isn’t sure.
Also EU leaders will be despondent that the UK under Corbyn’s plan may still not have made up its mind whether to stay or go by next spring, when the EU has to set its new budget. And for most EU leaders the Brexit uncertainty simply cannot be tolerated beyond April 2020.
Corbyn seems to be doing his best to gee up enemies and alienate potential allies.
What he could have done - rather than promise other opposition leaders he would be a temporary PM only long enough to secure a Brexit delay to accommodate a general election - was promise he would be a temporary PM long enough to oversee a Brexit referendum.
And only after a referendum would he go to the country in an election.
That might have scared Johnson, reassured EU leaders and persuaded other opposition leaders his priority is to stop a no-deal Brexit.
But what Corbyn has done will leave many scratching their heads about his true motivation.