What significant geopolitical event occurred early in Trump's presidency that concerned European allies?

Less than a month into Trump's presidency, an unprecedented gathering was orchestrated between American and Russian officials in Riyadh, Saudi Arabia, focused on Ukraine's future. This pivotal meeting included Secretary of State Marco Rubio and Russian Foreign Minister Sergei Lavrov discussing Russia's demands regarding NATO's 2008 membership promise to Ukraine. The talks created significant anxiety among European allies who were forced to watch nervously from the sidelines. Their concerns centered on the possibility of the US making deals with Russia that could potentially compromise European security interests, prompting discussions about increased military spending among EU nations.