Washington: In Virginia, Immigration and Customs Enforcement agents waited outside a church shelter where unauthorised immigrants had gone to stay warm. In Texas and in Colorado, agents went into courthouses, looking for foreigners who had arrived for hearings on other matters.

At Kennedy International Airport in New York, passengers arriving after a five-hour flight from San Francisco were asked to show their documents before they were allowed to get off the plane.

The Trump administration’s far-reaching plan to arrest and deport vast numbers of unauthorised immigrants has been introduced in dramatic fashion over the past month. And much of that task has fallen to thousands of ICE officers who are newly emboldened, newly empowered and already getting to work.

Gone are the Obama-era rules that required them to focus only on serious criminals. In Southern California, in one of the first major roundups during the Trump administration, officers detained 161 people with a wide range of felony and misdemeanour convictions, and 10 who had no criminal history at all.

“Before, we used to be told, ‘You can’t arrest those people,’ and we’d be disciplined for being insubordinate if we did,” said a 10-year veteran of the agency who took part in the operation. “Now those people are priorities again. And there are a lot of them here.”

Interviews with 17 agents and officials across the country, including in Florida, Alabama, Texas, Arizona, Washington and California, demonstrated how quickly a new atmosphere in the agency had taken hold. Since they are forbidden to talk to the press, they requested anonymity out of concern for losing their jobs.

The White House press secretary, Sean Spicer, said Tuesday that the president wanted to “take the shackles off” of agents, an expression the officers themselves used time and again in interviews to describe their newfound freedom.

“Morale among our agents and officers has increased exponentially since the signing of the orders,” the unions representing ICE and Border Patrol agents said in a joint statement after President Donald Trump issued the executive orders on immigration late last month.

Two memos released this past week by the Department of Homeland Security, the parent agency of ICE and the Border Patrol, provided more details about how it would carry out its plan, which includes Trump’s signature campaign pledge — a wall along the entire southern border — as well as speedier deportations and greater reliance on local police officers.

But for those with ICE badges, perhaps the biggest change was the erasing of the Obama administration’s hierarchy of priorities, which forced agents to concentrate on deporting gang members and other violent and serious criminals, and mostly leave everyone else alone.

A whirlwind of activity has overtaken ICE headquarters in Washington in recent weeks, with employees attending back-to-back meetings about how to quickly carry out Trump’s plans. “Some people are like: ‘This is great. Let’s give them all the tools they need,’” said a senior staff member at headquarters, who joined the department under the administration of George W. Bush.

But, the official added, “other people are a little bit more hesitant and fearful about how quickly things are moving.”

Two officials in Washington said that the shift — and the new enthusiasm that has come with it — seems to have encouraged pro-Trump political comments and banter that struck the officials as brazen or gung-ho, like remarks about their jobs becoming “fun.” Those who take less of a hard line on unauthorised immigrants feel silenced, the officials said.

ICE has more than 20,000 employees, spread across 400 offices in the United States and 46 foreign countries, and the Trump administration has called for the hiring of 10,000 more. ICE officers see themselves as protecting the country and enforcing its laws, but also, several agents said, defending the legal immigration system, with its yearlong waits to enter the country, from people who skip the line.

John F. Kelly, the secretary of the Department of Homeland Security, said in a statement after the first large-scale roundups of the Trump administration: “President Trump has been clear in affirming the critical mission of DHS in protecting the nation.”

“There is no greater calling than to serve and protect our nation,” he added, “a mission that the men and women of ICE perform with professionalism and courage every single day.”

Some of the more visible ICE operations in recent weeks have ricocheted around the internet, and sometimes drawn backlash. At Kennedy Airport, Customs and Border Protection agents checked documents of passengers getting off a flight from San Francisco because ICE, a sister agency, thought a person with a deportation order might be on the plane. They did not find the person they were looking for.

After the arrests outside the church in Alexandria, Virginia, Gov. Terry McAuliffe, a Democrat, wrote a letter to Kelly, saying the action “raises a concern that, unlike previous actions, ICE agents are detaining Virginia residents without cause or specific allegations of criminal activity.”

Bystanders are being taken in if they are suspected to be unauthorised, even if they have committed no crime, known within the agency as “collateral” arrests. While these arrests occurred under the Obama administration, they were officially discouraged, to the frustration of many agents. “Which part of illegal don’t people understand?” an agent in Arizona asked.