Senior politicians privately briefing foreign diplomats. Nothing new in that, it’s been happening for more than a century.

Senior politicians privately briefing foreign diplomats about the closely-held internal affairs of their party or government. Nothing new in that, but it’s edging closer to an ethical border.

Senior politicians privately briefing foreign diplomats about internal party or government affairs way ahead of the information becoming known to the politician’s senior colleagues. Doesn’t that get close to a conflict of interest?

But the key question to ask about Mark Arbib’s apparent role as a “valuable source of information on Labor politics” to the US Embassy in Canberra is: what’s in it for Arbib?

Is this about cosying up to the world’s superpower because it helps his political career to have their support? Is it ideological? Is there a quid pro quo?

If Arbib was happy to brief the US on what his party leader (and prime minister) was telling him privately about internal party matters, what other inside information was he prepared to share with a foreign government? Did he have approval of his leader or senior colleagues to pass such sensitive information to the US government?

Surely there must be a line, somewhere.