US president Donald Trump’s unorthodox use of Twitter during his election campaign and especially since taking office has flummoxed many governments around the world. The key questions foreign governments are asking is whether they should follow and mention the personal account of the president, @realDonaldTrump, or the institutional account, @POTUS, and how they should they engage with the president on social media.

Many world leaders tweeted the customary congratulations when Trump took office on 20 January. The @realDonaldTrump account is now followed by 137 world leaders, up from 97 at the end of January, while 226 world leaders follow the official @POTUS account.

Trump’s frequent use of Twitter presents unprecedented challenges to traditional diplomacy, and only a handful of world leaders have engaged directly with him on the platform. In one of her first radio interviews, Switzerland’s new president, Doris Leuthard, admitted she found Trump’s Twitter approach unexpected and worrying. “We will see if he calms down,” she said. The former German foreign minister and now president, Frank-Walter Steinmeier, acknowledged: “Every president needs to develop and coin their own style,” adding, “I can't imagine that tweets will be the way to go in the long run.”

The diplomatic community has been stunned by the presidential tweets and does not react directly to rebuke him, not wanting to pick a Twitter fight with the most powerful world leader. The UK Foreign Office stayed mum when President-Elect Donald Trump tweeted that former UKIP leader Nigel Farage “would do a great job” as the UK ambassador to the United States. While a spokesperson for No 10 was quick to explain that, “There is no vacancy. We already have an excellent ambassador to the US,” neither the Foreign Office nor the UK government reacted publicly on Twitter in an apparent attempt to downplay the diplomatic incident.

The Canadian government decided not to reply directly to Donald Trump’s tweet claiming that “Canada has made business for our dairy farmers in Wisconsin and other border states very difficult. We will not stand for this. Watch!” However, Prime Minister Justin Trudeau picked up the phone the following day to discuss bilateral trade issues with President Trump, and Foreign Minister Chrystia Freeland went on Bloomberg TV to address the looming trade war.

Pope Francis’s two most popular tweets are clear references to Donald Trump’s policies without mentioning the US president: “How often in the Bible the Lord asks us to welcome migrants and foreigners, reminding us that we too are foreigners!” he tweeted on 18 February; and “I invite you not to build walls but bridges, to conquer evil with good, offence with forgiveness, to live in peace with everyone,” posted on 18 March.

Only a handful of world leaders have directly addressed @realDonaldTrump on Twitter. On 1 June, European Council President Donald Tusk asked President Trump not to "change the (political) climate for the worse" and pull out of the Paris climate deal.

On 1 May 2017, Hilda Heine, the president of the Marshall Islands, had a similar message pleading with President Trump not to abandon the Paris agreement on fighting climate change: “From one President to another, staying in #ParisAgreement is best way to create jobs & grow economy. US has most to gain” she tweeted, as the US president declared May 2017 as Asian American and Pacific Islander Heritage Month.

The governor of Puerto Rico replied on Twitter to Trump’s tweet stating that “Democrats are trying to bail out insurance companies from disastrous #ObamaCare, and Puerto Rico with your tax dollars. Sad!” Ricardo Rosselló hit back: “The American citizens of Puerto Rico deserve to be treated fairly. Health and civil rights are not partisan issues.”

On the day President Trump issued the travel ban for citizens from a number of Middle East countries, Canadian Prime Minister @JustinTrudeau tweeted the exact opposite message: “To those fleeing persecution, terror & war, Canadians will welcome you, regardless of your faith. Diversity is our strength #WelcomeToCanada.” This not so subtle sub-tweet has become the most popular tweet of any world leader over the past 12 months, with 1.2 million likes and retweets.

Mexican President Enrique Peña Nieto, who is the 12th most followed world leader on Twitter with more than 6.3 million followers on his @EPN account, is so far the only foreign leader who has replied directly to one of Donald Trump’s tweets.

After a meeting with the candidate Donald Trump in September 2016, @EPN bluntly replied to Donald Trump’s tweet that “Mexico will pay for the wall!” explaining in Spanish that “Mexico would never pay for a wall”, a Twitter spat which has attracted more than 48,000 retweets.

After Donald Trump signed the executive order to build the border wall, the Mexican president posted a video reply on Twitter reiterating: “I’ve said time and again; Mexico won't pay for any wall. I regret and condemn the decision of the United States to continue construction of a wall that, for years, has divided us instead of uniting us.” He added that, “Mexico doesn’t believe in walls.” When President Trump replied in a tweet that: “If Mexico is unwilling to pay for the badly needed wall, then it would be better to cancel the upcoming meeting,” Peña Nieto promptly cancelled the meeting in a tweet.

Swedish Deputy Prime Minister Isabella Lövin tweaked President Trump by posting a picture signing a climate bill surrounded by her female staffers, a subtle reference to the pictures from the White House showing the US president surrounded by an all-male staff when signing an executive order barring US federal funding for foreign NGOs that support abortion.

At their recent meeting in Bergen, the five Nordic prime ministers from Norway, Finland, Sweden, Denmark, and Iceland openly mocked Donald Trump’s orb picture with Saudi Arabia’s King Salman. Norway’s Prime Minister Erna Solberg shared both pictures on her Facebook page with the caption: “Who rules the world? Riyadh vs Bergen.”

The full Twiplomacy Study 2017 is available here.