This is the second posting on immigraiton policy in a second Trump administration. This one addresses an important legal power which Trump did use in the first time and will surely expand on in a second term.
Section 212(f) of the Immigration and Nationality Act of 1952 grants the President of the United States broad authority to suspend the entry of certain classes of aliens into the U.S. President Trump used it in 2017, the Supreme Court backed him, and he will surely use it more broadly if re-elected. He can basically shut down most of the immigration flow in to the country using this provision.
Text of Section 212(f): Whenever the President finds that the entry of any aliens or any class of aliens into the United States would be detrimental to the interests of the United States, he may, by proclamation, and for such period as he shall deem necessary, suspend the entry of all aliens or any class of aliens as immigrants or nonimmigrants, or impose on the entry of aliens any restrictions he may deem to be appropriate.
When it was used: Ronald Reagan,1986: to suspend entry of Cuban nationals as immigrants or nonimmigrants. George H.W. Bush, 1990: to suspend the entry of certain Panamanian officials. Bill Clinton, 1994: to suspend the entry of Haitian nationals. George W. Bush, 2011: post-9/11 to suspend the entry of individuals engaged in terrorist activities. Barack Obama, 2011: to suspend the entry of individuals involved in human rights abuses in Syria and Iran. Donald Trump: multiple times, notably in the January, 2017 travel ban for Iran, Iraq, Libya, Somalia, Sudan, Syria, and Yemen (the “Muslim ban’).
In 2018, the Supreme Court weighed in on a revised Executive Order to the January 2017 ban, in Trump v. Hawaii. The 5 – 4 majority said that it was a legitimate exercise of the president’s authority under immigration laws to suspend entry of aliens into the U.S, that the proclamation was neutral on its face regarding religion (that is, was not a violation of the 1st Amendment), and had a legitimate purpose of preventing entry of those who could be “detrimental to the interests of the United States” (noting the exact language of 212f).