Trump left Charlevoix before the G-7 summit had concluded in order to attend the bilateral summit in Singapore with North Korean leader Kim Jong-un.
Some Twitter users did not agree with Bolton's opinion, criticizing Trump's policies and the way his administration deals with USA allies.
An official White House photograph from the summit shows Trump holding forth as Merkel, Canadian Prime Minister Justin Trudeau and Prime Minister Shinzo Abe of Japan listen.
Dennis Rodman broke down in tears talking about North Korea-US situation
Rodman first visited North Korea in 2013 when he toured the country with the Harlem Globetrotters. And obviously he has a great rapport with Kim Jong Un - who is a basketball fanatic himself .
Many Twitter users took up the challenge of a caption contest and offered alternatives to Merkel's straightforward description.
Mr Trump on Saturday threw the G-7's efforts to show a united front into disarray after he became angry with Mr Trudeau, and said he might double down on import tariffs by hitting the sensitive auto industry.
"(Trump's) withdrawal via Twitter is of course sobering and a little depressing", Merkel said, according to a translation from public broadcaster Deutsche Welle.
US trading partners are furious over Trump's decision last week to impose tariffs on steel and aluminum imports from Canada, the European Union and Mexico as part of his "America First" agenda.
"Europe must take its fate into his own hands and no longer imprudently follow the US", Merkel said.
Supreme Court approves Ohio's method of purging voter rolls
The state appealed, saying the process targets people who have failed to respond to a notice, not those who have failed to vote. If the notice is ignored and the voter fails to update a registration over the next four years, the registration is canceled.
The Republican firebrand also lashed out against Canada's Prime Minister Justin Trudeau saying he "acts out when called out". Asked by reporters whether he would relent on tariffs, Trump looked at Merkel and said: "I don't know".
The summit ended in disarray: US President Donald Trump said the US would not endorse the joint statement from the summit.
That statement had sought to overcome deep disagreements, notably over trade.
However, Merkel said it is too early to give up entirely on the United States and "There are still good reasons to continue our fight [aimed at keeping a close transatlantic partnership], even though we can not just rely on it anymore".
Trump said that his ultimate goal was the elimination of all trade duties.
France's Macron seeks to forge European front against Trump
Trump focused his conversation with Macron on German trade for about 15 minutes in the one-hour meeting. In the past, the US has had low points with Europe.