I think the key issue here is a formal one. Trump is not yet president; he hasn’t taken the oath. How can he send Kellogg if he isn’t officially the head of the US executive branch, which is still led by [current President Joe] Biden?

KYIV, Ukraine (AP) — An upcoming trip to Kyiv by U.S. President-elect Donald Trump’s special envoy for Ukraine and Russia has been canceled but will be rescheduled, Ukrainian Foreign Minister Andrii Sybiha said Tuesday.

Kyiv and Washington are currently determining the new day of the visit. “I am confident that this meeting will take place in due time, and we are in contact to quickly determine the timeframe for holding this meeting and filling it with national interests,

Keith Kellogg, US President-elect Donald Trump's special envoy for Ukraine and Russia has postponed his planned trip to Kyiv and other European capitals until after Trump's inauguration on 20 January.

Kellogg was initially scheduled to visit Kyiv in early January to meet with Ukrainian leaders, and his team also planned meetings with officials in other European capitals, including Rome and Paris. But his "fact-finding trip,