WARSAW — 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.

NATO allies have been bracing for US support for Ukraine to shrink over the next year. Trump has questioned the value of aid to Ukraine and the US commitment to NATO, and while he has said he wants to end the war he has not yet weighed in on whether his administration will continue providing military assistance to Ukraine.

Ahead of the imminent transfer of power, the US has worked to transition aid to Ukraine from a US-led effort to a NATO-led mechanism in part to “Trump-proof” the assistance, CNN has reported.

“That work is ongoing, with NATO shouldering more and more responsibility every day,” said O’Donnell, a spokesman for NATO’s Supreme Headquarters Allied Powers Europe.

The Biden administration has tried to leave Ukraine in the strongest possible position as it prepares for the incoming Trump administration, both on the battlefield and in the event of negotiations. On Thursday, the US announced another $500 million military aid package for Ukraine, the final expected package from the outgoing leadership.

Over the past month, NATO has slowly begun taking over responsibilities from the US effort to assist Ukraine, known as Security Assistance Group-Ukraine (SAG-U), which handled the flow of Western weapons and equipment to Kyiv. Air defenses in Poland, now under the command of NATO, are a key part of protecting the logistics hubs that enable the flow of those weapons.

Another critical element in aid to Ukraine has been the US-led Ukraine Defense Contact Group (UDCG), a meeting of approximately 50 countries that have supported Ukraine with weapons and equipment.

US Defense Secretary Lloyd Austin led the Biden administration’s last meeting of the UDCG at Ramstein Air Base in Germany on Thursday, challenging the other countries to keep the forum alive. It is not yet clear whether the Trump administration will continue to chair the forum, or whether a European country will have to take over.

“We must not stop now,” Austin said at a news conference on Thursday. “The coalition to support Ukraine must not flinch. It must not falter. And it must not fail.” — CNN