U.S. President Donald Trump and Russian President Vladimir Putin are meeting face-to-face in Alaska on Friday for a high-stakes summit that could determine the trajectory of the war in Ukraine and the fate of European security.

Trump’s allies have cast the U.S. president as a heavyweight negotiator who can find a way to bring the slaughter to a close, something he used to boast he could do quickly. For Putin, a summit with Trump offers a long-sought opportunity to try to negotiate a deal that would cement Russia’s gains, block Kyiv’s bid to join the NATO military alliance and eventually pull Ukraine back into Moscow’s orbit.

There are significant risks for Trump: By bringing Putin onto U.S. soil, the president is giving Russia’s leader the validation he desires after his ostracization following his invasion of Ukraine 3 1/2 years ago. Any success is far from assured, especially as Russia and Ukraine remain far apart in their demands for peace.

What to know about the U.S.-Russia summit:

What to expect: Trump has threatened “very severe consequences” if Putin does not agree to stop the war after the summit. Putin sees the meeting as a chance to cement Russia’s territorial gains and keep Ukraine from hosting any Western troops so that Moscow can gradually pull the country back into its orbit.

What Russia and Ukraine want: Putin demands Kyiv cede the regions Moscow annexed in 2022, even though Russia doesn’t fully control them, and recognize Crimea, illegally annexed in 2014, as part of Russia. Putin also wants Ukraine to renounce its effort to join NATO, limit its armed forces and recognize Russian as an official language along with Ukrainian. Zelenskyy insists any peace deal must be acceptable to his people and include robust security guarantees against future Russian aggression.

Ukraine not invited: The exclusion of Zelenskyy is a blow to the West’s policy of “nothing about Ukraine without Ukraine.” Trump suggested that he could bring Zelenskyy to Alaska for a subsequent, three-way meeting, though Russia has not agreed to this.