What are the concerns about potential diplomatic negotiations between the US and Russia regarding Ukraine?

For nearly three years, Russia has been isolated by Western sanctions following Putin's invasion of Ukraine. Now, with diplomatic talks occurring between US and Russian officials, many in Europe fear that Putin may secure a deal with President Trump that effectively rewards Russia with Ukrainian territory without providing Ukraine adequate security guarantees. This scenario is particularly concerning as it could leave Ukraine vulnerable to future Russian aggression. Critics worry such an arrangement might allow Putin to reinvade Ukraine later, while simultaneously giving Russia diplomatic recognition and relief from international isolation. Ukrainian leadership has emphasized that any agreements about their country should not be made without their direct involvement in negotiations.