U.S. President Joe Biden's move this week to block migrants at the U.S.-Mexico border aims to reduce the record numbers of crossings and shield him from Republican criticism, but is a turn away from his campaign promise to restore access to asylum.

Initial backlash to Biden's policy shift also signals it could be challenged in court, from both those who favor restricting immigration and advocates for asylum-seekers.

The Democratic president on Thursday announced a new two-pronged strategy that pairs deterrence measures blocking Cuban, Haitian and Nicaraguan migrants at the U.S.-Mexico border while opening new legal, limited pathways into the United States for them.