Merkel said the contentious meeting drives home the point she's made for more than a year: that the European Union needs to stand together to increase its clout on the world stage and that the U.S. is a less reliable partner. Or we'll stop trading with them.
Kudlow also accused Trudeau of trying to undermine the US president at a critical time before his summit with the reclusive Kim on Tuesday.
Speaking to reporters from her home country, German Chancellor Angela Merkel called the US' retraction of support for a shared statement "sobering and somewhat depressing".
After Trump departed for Singapore for a highly anticipated meeting with North Korean leader Kim Jong Un, Trudeau criticized Trump for triggering a trade dispute and said Canada would retaliate with tariffs against the U.S.
Saying Trudeau is "dishonest & weak", he also threatened "tariffs on automobiles flooding the U.S. Market!"
Trump repeated that America's allies had repeatedly won on trade deals, hurting American workers and jobs.
The Prime Minister said the United Kingdom still wanted to discuss a post-Brexit trade deal with the USA and said Mr Trump was still looking forward to July's visit to Britain.
"There are still good reasons to continue our fight [aimed at keeping close transatlantic partnership], even though we can not just rely on it anymore", she added.
"Fair trade now fool trade", Trump vents anger on North Atlantic Treaty Organisation allies, Trudeau
"That's what matters", he wrote.
"Worldwide cooperation can not depend on fits of anger or little words".
Germany also said it will stand by the jointly agreed communique.
President Donald Trump told French President Emmanuel Macron that the European Union is worse than China on trade during a conversation that portended the tense end to this year's G7 summit.
Officials from European delegations quickly leaked copies of the joint statement, and it was published online moments before Trump tweeted. "And I think we should have a reciprocal tax", the United States president said. But before he left a text had already been agreed that emphasised that on climate change the G7 has become a G6, with separate paragraphs setting out the differing positions of the USA and Canada, France, Germany, Italy, Japan, the United Kingdom and the EU.
Last year, the U.S. president was wowed by a French military parade in Paris after being invited to join Mr Macron for his country's annual Bastille Day celebrations.
Former Belgian Prime Minister Guy Verhofstadt posted a now infamous G-7 photo with the following caption: "Just tell us what Vladimir has on you. And so we are talking to many countries", Trump said.
Secretary of State Mike Pompeo praised European countries for helping to bring about the North Korea summit, alluding to their enforcement of sanctions against Pyongyang. "They know it", he insisted in his departing news conference. I think it's great that they can get away with it.
"It's actually not a real surprise". He says that we are the problem with tariffs.