President Trump’s reinvigorated effort to secure the Mexican border coincides with the acceleration of his 2020 reelection bid and comes as some immigration hawks say the administration has failed to realize a signature campaign promise.

Trump on Monday said the federal government would begin releasing undocumented immigrants in sanctuary cities, a provocative move to pressure Democrats in Congress to negotiate and that follows a bold house cleaning of top personnel at Homeland Security. The president wants the department to toughen its response to a historic surge of asylum-seekers and unlawful immigrants, vexing problems that persist despite his vow to halt illegal crossings.