The president hosted leaders of Poland at the White House as he sought to reassure NATO members of American steadfastness in the face of threats from Moscow and former President Donald J. Trump.
The attacks and drone strikes across the southern border were intended to counter President Vladimir V. Putin’s control over Russia, a leader in one of the groups said.
The African nation said it would not send a force until Haiti forms a new government after the Haitian prime minister announced his intention to resign.