WASHINGTON — The Obama administration on Thursday officially scrapped the last vestiges of a U.S. registration system for Muslim immigrants. If President-elect Donald Trump now wants to introduce an expanded version of the program, he will have to start from scratch.

The post-9-11 registration program for immigrant men arriving mainly from the Islamic world hasn’t been enforced since 2011. Although it never prohibited travel for men and boys from the more than 20 affected countries, including Syria, Iraq and Afghanistan, Trump’s suggestions about banning Muslim immigrants from the United States have led to fears that it could be reinstated and used for new and enhanced purposes.

The decision to erase it from the books entirely marks one of President Barack Obama’s last administrative actions on immigration and will at least slow any Trump effort to introduce even tougher requirements, as has been suggested by a top adviser.

The registration program is “not only obsolete,” said Neema Hakim, spokesman for the Homeland Security Department, “its use would divert limited personnel and resources from more effective measures.”