First, it was then-candidate Donald Trump's campaign trail contention that Chancellor Angela Merkel was "ruining Germany" with her decision to allow in more than 1 million asylum-seekers in 2015 and 2016.
Stoltenberg said North Atlantic Treaty Organisation should focus for now on reaching the 2 percent goal by 2024, something just five of the 29 nations have done.
Bulgarian President Rumen Radev confirmed that Trump had made the demand and asked what it meant for the future of the alliance that has been the bedrock of European security for 70 years.
"This need not presage a darker time, like Rome's withdrawal from Britain, but more will be required of the world's other free countries".
The alliance set a goal in 2014 for each country to reach the 2% of GDP spending target by 2024. The criticism and proposal dominated headlines with leaders, including Secretary General Jens Stoltenberg, widely accepting the complaint of unequality and pledging to spend more.
"Germany is a captive of Russia because it is getting so much of its energy from Russia", Mr Trump said, taking aim at the proposed Nord Stream II gas pipeline, which he has previously criticised.
"We have to talk about the billions and billions of dollars that's being paid to the country we're supposed to be protecting you against", Trump said, referring to European purchases of Russian natural gas. The vast undersea pipeline is opposed by the USA and some other European Union members, who warn it could give Moscow greater leverage over Western Europe.
German Chancellor Angela Merkel (L) looks on as US President Donald Trump speaks to other leaders as they pose for a family photo at the Park of the Cinquantenaire during the NATO Summit in Brussels, Belgium July 11, 2018.
Photographer gets caught up in Croatia's celebration... and then receives a kiss
Speaking to Sky News 22 years on, the ex-footballer said: "Football's coming home, I couldn't listen to it for 20 years, frankly". Now England have to pick themselves up to face Belgium in the third place play-off against Belgium in St Petersburg on Saturday.
The pair later met for a one-on-one meeting and while Trump insisted they had a "very very good relationship", their frosty body language suggested otherwise.
At the same time, despite his criticism of the pipeline and its links to Russia, Trump has been noncommittal in recent comments about whether he might lift USA sanctions on Russia, and told reporters he'd "have to see" whether the US might recognize Crimea to be part of Russia.
Trump told reporters during brief remarks at the end of the meeting that the two had a "very, very good relationship" and congratulated Merkel on her "tremendous success".
Trump's condemnation of Germany also highlighted his determination to turn the tables on his critics, at a distance if not in person.
Earlier, Mr Trump criticised Germany over its defence spending and energy reliance on Russian Federation.
NATO Secretary General Jens Stoltenberg at a news conference following the summit: "We all agree that we do not have fair burden-sharing in our Alliance today".
Arriving at Nato, Ms Merkel sought to put her countries ties to the western alliance in historical context.
Trump's harsh words for Merkel, whose country has hosted tens of thousands of USA troops that have been key to post-WWII stability in Europe for seven decades, struck at the core of the alliance.