Matt Whitaker, the United States ambassador to NATO, said Sunday that Ukrainian President Volodymyr Zelenskyy could end up joining the high-stakes meeting between President Trump and Russian President Vladimir Putin. Mr. Whitaker said Mr. Trump will have the final say on who is invited to the meeting on Friday in Alaska and that there is ample time between now and then to make that decision. “Yeah, I certainly think it is possible,” Mr. Whitaker said on CNN’s “State of the Union” when asked whether Mr. Zelenskyy could make an appearance. “Certainly, there can’t be a deal that everybody that is...