Trump, as immigration reporter Dara Lind explained at Vox, cannot physically stop anyone from illegally entering the United States, but he can close ports of entry, which would prevent “people and goods from legally entering the country.”
Political symbolism is similarly thought to have been the motivating factor for Nixon’s Operation Intercept.
Launched in 1969 and lasting just 20 days, Operation Intercept was ostensibly meant to stem the flow of illegal drugs, including marijuana, into the United States. The idea was to add agents to the border to help better intercept the contraband. “In reality, however, it was designed not to interdict narcotics but to publicize the new administration’s war on crime and force Mexican compliance with Washington’s anti-drug campaign,” political science professor Richard B. Craig wrote in 1980.
At the time, newspapers deemed it the “largest peacetime search and seizure operation in history.” The operation was planned by G. Gordon Liddy, the former FBI agent who later helped orchestrate the Watergate break-in; the State Department was effectively shut out of the planning process for the operation.
Operation Intercept resulted in a “near shutdown of traffic” across the southern border. There were major backups at the border; instead of random searches, everyone was searched; legal laborers and commerce couldn’t cross; and Mexico, in response to this unilateral approach to a bilateral issue, began a boycott of U.S. goods. Also, almost no marijuana was actually seized; traffickers just found other, safer ways in.
About three weeks later, the United States abandoned the plan in favor of Operation Cooperation with Mexico. Some suggest that the plan worked — Mexico, the thinking goes, was more keen to cooperate with the United States after Operation Intercept. Others suggest that Operation Intercept had lasting international consequences and serves as a cautionary tale against unilateral action on multilateral issues.
In 2019, Trump seems to have taken the first lesson, or at least to not be perturbed by potential international ramifications; he also ordered the suspension of aid to three Central American countries — El Salvador, Guatemala and Honduras — to pressure their governments to stop migration to the United States.