What is the primary fear European leaders have about potential Trump-Putin negotiations?

European leaders primarily fear that Trump might rush into a deal with Putin that neglects European security interests while effectively rewarding Russia's aggressive behavior. They are concerned such an agreement would not only sideline Europe's strategic concerns but could potentially embolden Russia to make further threatening moves against neighboring countries in the future. This anxiety stems from recent talks in Saudi Arabia involving American and Russian officials that excluded Ukraine, raising concerns about decisions being made without considering all affected parties. European leaders worry that hasty concessions could undermine regional security architecture and validate Russia's aggressive foreign policy approach.