P resident Donald Trump is scheduled on Monday to welcome Ukrainian President Volodymyr Zelenskyy to the White House for a high-stakes meeting as the U.S. president pushes for a deal to end Moscow's war on its neighbor. A host of European leaders will join the pair.

Any changes to Ukraine's territory would have to be settled in Ukraine by a referendum, according to the country's constitution.

After rolling out the red carpet for Russian President Vladimir Putin in Alaska on Friday, Trump said an agreement should be struck to end the 42-month-long war which has killed tens of thousands and ...