President Donald Trump has enacted a significant new travel ban, barring individuals from 12 predominantly Muslim-majority and African nations from entering the United States.

This move, announced Wednesday, resurrects one of the most controversial policies from his first term and comes in the wake of a recent attack in Colorado that targeted an event supporting Israeli hostages.

Concurrently, Trump signed a separate proclamation suspending the visas of foreign students intending to participate in exchange programs at Harvard University.

The newly implemented travel ban, detailed in a presidential proclamation, covers Afghanistan, Myanmar, Chad, Republic of the Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Somalia, Sudan, and Yemen.

The measure also imposes partial entry limitations on individuals from Burundi, Cuba, Laos, Sierra Leone, Togo, Turkmenistan, and Venezuela.

In a video posted on social media Wednesday, President Trump linked the ban to the recent Colorado attack, stating:

The recent terror attack in Boulder, Colorado, has underscored the extreme dangers posed to our country by the entry of foreign nationals who are not properly vetted, as well as those who come here as temporary visitors and overstay their visas. We don’t want them.