By ELLIOT SPAGAT
SAN DIEGO (AP) -- U.S. Customs and Border Protection officers will be key players in putting President Donald Trump's revised travel ban into effect on Thursday, affecting visitors from six mostly Muslim countries.
They are the officers dressed in blue who are stationed at airports and border crossings and screen people coming into the U.S. They stamp passports, inspect travel documents, confiscate drugs and other illicit items and make sure belongings and purchases are properly declared.
Customs and Border Protection officers were embroiled in chaos when an earlier version of President Donald Trump's travel ban took effect, forcing them to turn away visa holders who were later allowed in. They will be in the mix again for the new ban affecting visitors from Syria, Sudan, Somalia, Libya, Iran and Yemen.
Here's a look at what they do:
WHAT IS CUSTOMS AND BORDER PROTECTION?
The agency was created as part of the Department of Homeland Security in 2003 after attacks on the World Trade Center and Pentagon. Its largest division -- the Office of Field Operations -- admits people and goods at 328 airports, land crossings and seaports. They admitted 390 million travelers during the fiscal year that ended Sept. 30, including 119 million at airports.
Much of the work done by the agency is at border crossings along the U.S.-Mexico border.
The busiest point of entry is San Diego's San Ysidro crossing with Tijuana, Mexico, with 31.8 million admissions during the latest 12-month period, an average of 87,000 a day. El Paso, Texas, across from Ciudad Juarez, Mexico, was second-busiest with 28.8 million admissions, followed by San Diego's Otay Mesa crossing (17.8 million), Laredo, Texas (17.7 million), and New York's John F. Kennedy International Airport (15.9 million).
The travel ban will mostly affect airports because that's how visitors from the six countries generally arrive. Aside from JFK, the only airports to crack the top 20 in passenger volume are Miami International (No. 11), Los Angeles International (No. 12) and San Francisco International (No. 20).
HOW WILL OFFICERS ENFORCE THE TRAVEL BAN?
Senior officials from the departments of State, Justice and Homeland Security labored Wednesday to finalize rules on who gets in. Homeland Security has said only that it will enforce the ban "professionally, with clear and sufficient public notice."
Monday's Supreme Court ruling to partially reinstate the ban exempts visitors who prove a "bona fide relationship" with a U.S. person or entity. Government lawyers must decide how to define that. The court offered only broad guidelines, suggesting they would include a relative, job offer or invitation to lecture.
The union that represents Customs and Border Protection officers said Tuesday it wanted the administration to provide detailed guidance to help avoid a repeat of the chaos that ensued in January when an initial ban was announced.
In a statement, the agency said it is working closely with the State and Justice Departments on how to implement the order. The task falls largely to State but Customs and Border Protection officers would get involved if someone from one of the six countries arrived without a visa or there was a reason to question the validity of their documents.
WHAT ILLEGAL ACTIVITY DO OFFICERS FIND?
Agents primarily seize drugs and stop people seeking to enter the country illegally.
Drugs -- increasingly heroin and methamphetamine -- are commonly smuggled into the United States by car from Mexico. People enter the country illegally by hiding in trunks or by using someone else's travel documents.
Officers denied admission 274,821 times at airports, land crossings and seaports during the latest fiscal year, an increase of 8 percent from the same period a year earlier. They seized 257 tons of marijuana, 26.3 tons of cocaine, 18.8 tons of methamphetamine and 2.1 tons of heroin.
An estimated 40 percent of people in the country illegally overstay their visas, and one of the agency's top priorities is to better track them. The absence of a system for people to check out when the leave the country makes that a daunting and expensive endeavor. Homeland Security said in May that nearly 740,000 foreigners overstayed visas during the latest fiscal year, and that was only for those who arrived by plane or ship.
IS IT DIFFERENT THAN BORDER PATROL?
The Border Patrol is another division within the agency. Customs and Border Protection agents wear blue uniforms and patrol ports of entry. Border Patrol agents work areas between and wear green uniforms.
Customs and Border Protection is the nation's largest law enforcement agency, with about 60,000 employees and an annual budget of $13.5 billion. Trump has requested 21 percent spending increase, partly to build a wall on the border with Mexico and hire more Border Patrol agents.
WHAT ABOUT THE STAFFING SHORTAGE?
The Trump administration said this month that it has 1,400 vacancies for officers at ports of entry. Customs and Border Protection has struggled to fill jobs for years, largely because an unusually high number of applicants fail a pass a polygraph that has been a hiring requirement since 2012. One official recently said 75 percent failed, more than double the average among law enforcement agencies surveyed by The Associated Press.
The House of Representatives passed a bill this month to waive the polygraph requirement for many veterans and some other applicants. Customs and Border Protection recently said it was easing some physical fitness and language requirements in hiring.
The administration has called for expanding the Border Patrol by 5,000 agents but has not proposed any increase in officers at airports, land crossings and seaports.
Associated Press writers Alicia A. Caldwell and Matthew Lee in Washington contributed to this report.