Trump's "job is to bridge" the parties in the conflict, Fleitz told ABC News, and test whether Putin is sincere about wanting an end to the war. Fleitz said he thinks Trump will have a "very critical eye" toward Putin and be "very quick to implement sanctions" if he judges Putin to be playing him.

Donald Trump and Vladimir Putin hold talks in Alaska on Friday, focused on the U.S. president's push to seal a ceasefire deal on Ukraine but with a last-gasp offer from Putin of a possible face-saving nuclear accord on the table too.

Follow live updates as Trump and Putin convene in Alaska to discuss what's next in the Ukraine war. Trump has pushed the countries toward a peace deal in recent months.