The talks on Friday in Alaska pull the Russian leader out of diplomatic isolation from the West, and Ukrainian and European leaders fear it gives him an opening to sway the American president.

President Trump set a low bar for his summit with President Vladimir V. Putin of Russia, saying he was ready to walk away if no deal was forthcoming.

The U.S. president is pushing to end the war in Ukraine, but analysts say the Russian leader could turn a hastily planned meeting to his advantage.