Now, Merkel is suggesting that the Americans aren't really in, and, by extension, Germany and Europe are likely to take on a much more substantial and independent role than they have in the past 70 years.
Merkel's comment about what she has experienced in the past few days is a clear reference to Trump's disastrous European tour.
Her belief that the United States is no longer a reliable partner is a direct result of Trump's words and actions.
The keystone of Nato is Article 5, which has typically been read as a commitment that in the event that one member of the alliance is attacked, all other members will come to its aid.
When Trump visited Nato, he dedicated a plaque to the one time that Article 5 has been invoked - when all members of Nato promised to come to the United States' support after the attack on September 11, 2001. However, Trump did not express his commitment to Article 5 in his speech to Nato, instead lambasting other Nato members for not spending enough money on their militaries.
When Trump went on to the Group of Seven meeting in Italy, he declined to recommit to the Paris agreement on climate change, leaving the other six nations to issue a separate statement.
This cements the impression of the United States as an unreliable partner.
Trump has ostentatiously refused to express his commitment to an agreement that has been the bulwark of Europe-US security relations over the past three generations. He also has declined to say that the US will work within the previously agreed framework on global warming.
While many authoritarian states are cheered by Trump's election and actions, since he is unlikely to press them on human rights and other sore points, traditional US allies are enormously disheartened.
Merkel's rhetoric is clearly intended to imply that as the transatlantic relationship grows weaker, the European Union will grow stronger.
When she links Britain's departure from the European Union with US unreliability, she suggests that now that Britain is gone, it will be possible for the EU to concentrate on getting its own affairs in order, propelled by a stronger relationship between Germany and France.
Britain always wanted to keep transatlantic security institutions, such as Nato, strong, which sometimes meant pushing back against giving the EU a new security role. Now that Britain is no longer going to be part of the EU, it will no longer have veto power.
However, Merkel will face her own challenges in building a stronger Europe. Europe faces several internal disagreements. States such as Poland and Hungary agree more with Trump than with Germany on many issues. Southern European countries still resent Germany's support of painful and (for them) damaging austerity policies.
If Germany wants to cooperate with France on security, France is likely to look to Germany to make concessions on economic governance and spending. Although Merkel has recently hinted that such concessions might be possible, they will be controversial with other German politicians (including senior members of her party) and perhaps with the German public.
Finally, the criticisms offered by Trump (and many US leaders before him) are not entirely wrong - European states spend much less on their militaries than the United States does on its military and have effectively outsourced much of their defence to US armed forces.
Still, it is important to note that Merkel's temperament is the polar opposite of Trump's.
She is highly cautious. This speech is not an impulsive move.
Instead, Merkel is starting to make the case for a different EU, one that is stronger, more self-reliant and disinclined to look to the US for leadership. If she wins the upcoming German election decisively and is able to secure enough agreement from other European states to isolate the naysayers, she may set in motion a substantial long-term shift in the EU-US relationship.
People have not yet seriously begun to think through the consequences of Trump's election for global politics.
In some parts of the world, it is creating great opportunities.
States whose interests clash with the US may now have opportunities to win gains while the US, the global hegemon, is distracted with its internal crises.
In other parts of the world, allies are likely to recalibrate their behaviour, and in particular their dependence on the US. They will not want their security to entirely rely on a country that can elect a president as erratic as Trump is and hence will start to hedge their bets.
If the current US administration has decided that it no longer needs to rely on allies as much as in the past, those allies are deciding that they cannot rely on the US anymore and are starting to forge their own arrangements, which will diminish the US ability to influence their actions and decisions.