Hillary Clinton’s 2016 campaign chairman has responded to a tweet from Donald Trump, calling the President a “whack job” and telling him to “get a grip”.

Mr Trump is in Germany this week for what is expected to be a contentious G20 meeting after he announced that he would pull back from the Paris climate accord, an international agreement that took years to forge. In one of his tweets from Hamburg, Mr Trump claimed that “Everyone here is talking about why John Podesta refused to give the DNC server to the FBI and the CIA. Disgraceful!”

It’s unclear why the President was bringing up the 2016 election issue so publicly at the summit, or even if world leaders were truly discussing Mr Podesta refusing to hand over servers from the Democratic National Committee — an organisation that Mr Podesta was not working for during the 2016 election, as he was with the Clinton campaign.

“Get a grip man, the Russians committed a crime when they stole my emails to help get you elected President,” Mr Podesta tweeted in a string of jabs at the President. “Maybe you might try to find a way to mention that to [Russian President Vladimir] Putin.”

“Dude get your head in the game. You’re representing the US at the G20,” he finished.

Other American politicians joined in to criticise the Twitter friendly President.

“Yes, I’m sure that’s the big talk at G20. Not climate change or trade, but why didn’t John Pedestal give a server that wasn’t his to the CIA,” Democratic California Congressman Adam Schiff tweeted.

Mr Podesta’s private email account was hacked last March by what the former campaign chairman said were Russian sources. The emails were released on the whistleblower platform WikiLeaks in a series of dumps in October, in the weeks before Election Day.

While the emails didn’t contain any particularly salacious material, the email dumps were obsessed over by some media outlets, which picked through the emails hoping to find interesting nuggets on the inner-workings of the Clinton campaign.

Emails had already become a bad word for the Clinton campaign, however. Ms Clinton was dogged during the primaries and general election by concerns that she had used a private email server while serving as US secretary of State during the administration of former President Barack Obama. Those servers, which was investigated by the FBI, fuelled the narrative that the Clintons work in secrecy within Washington, a storyline that has been around since Bill Clinton was in the White House.