Within hours of the former Scottish Labour leader, Johann Lamont, announcing her resignation, a cartoon began to circulate on Twitter attacking the frontrunner in the race to succeed her.

Halloween themed, it depicted a ghoulish-looking Jim Murphy wearing a badge simply stating "I love Israel".

Supporters of the shadow international development secretary know his opponents will "go with everything they've got" to halt his bid to become Labour's leader north of the border, and ultimately Scotland's first minister after the parliamentary elections in 2016.

His backing for Israel, says one, will be conflated with his support for the Iraq war and Trident renewal to depict him as a right-wing, Westminster-based Blairite, out-of-touch with the supposedly more left-wing Scottish political scene.

Mr Murphy, MP for East Renfrewshire and a former chair of Labour Friends of Israel, has long been unapologetic in his defence of the Jewish state. Last month he was one of eight members of the shadow cabinet who defied Ed Miliband and stayed away from the vote on Palestinian statehood.

"Jim's no fair-weather friend of Israel," argued one party insider. "He's been a strong supporter not just when some perceived that to be politically expedient when Tony Blair was leader, but also, over the last four years, when it's been much tougher because of the stance of the leadership.'

Indeed, suggests another, while Mr Murphy derives some political benefit from his stance among the large Jewish community in his southern Glasgow seat, it has generally not been beneficial to him otherwise: "It's important people realise he's taken a hit for doing the principled thing".

John McTernan, Tony Blair's former political secretary and a former special adviser to Mr Murphy, deems attacks on his former boss' support for Israel and work against antisemitism "the politics of the gutter". He said: "My advice to Jim would be to unmask any attempt to attack him for what it is - prejudice."

Mr Murphy's task over the six weeks is complicated by the fact that the new leadership election rules introduced by Ed Miliband to curb the power of the unions have not been adopted in Scotland. There, the old electoral college, in which unions, party members, and parliamentarians each share a third of the votes, will decide his fate.

The Scottish TUC has a well-earned reputation for its hostility to Israel. Unison has already endorsed Neil Findlay - Mr Murphy's left-wing opponent.

Mr Murphy and Mr Miliband have never been close, and his relationship with shadow foreign secretary Douglas Alexander has soured. The pair jointly managed David Miliband's campaign for the party leadership four years ago, but have clashed over Mr Alexander's more hostile line on Israel and also over the decision not to back air strikes in Syria last summer.

But with a recent poll
predicting electoral meltdown for Labour in Scotland, Mr Miliband and Mr Alexander, know their hopes next spring may well rest on Mr Murphy stemming the tide of opposition in its for-mer bastion.