Caroline Beresford, Wellington's second-ranked diplomat in the US, tweeted "get your shit together" discussing Bernie Sanders-Elizabeth Warren Democratic ticket against Trump in the 2020 election.
"Please get your shit together or we will all die," she wrote in tweets, since deleted, later adding: "They've learned nothing."
Sanders and Warren are a liberal dream team but pundits would expect them to struggle against Trump's right-wing populism in the next presidential race.
It said Beresford's tweets were prompting "appropriate action".
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