NATO has taken over air defenses in Poland from the US just days before the inauguration of President-elect Donald Trump, according to a NATO spokesman, with questions looming about the incoming administration’s approach to the alliance and to Ukraine.

NATO assumed command and control from the US on Thursday, said Col. Martin O’Donnell, and will help to safeguard logistics nodes in Poland that are needed to continue delivering aid crucial to Ukraine’s war effort against Russia. The move is part of a broader effort that has been in the works for months to shift the burden of helping Ukraine from the US to European countries, amid questions over whether US support would continue under the Trump administration.