ICE was created by laws enacted in the immediate aftermath of 9/11. The laws that many people said had been cooked up in advance, and 9/11 provided the emergency* to get them passed. ICE was a key part of the new Department of Home Security.
Previously, INS handled both immigration services and immigration enforcement. Originally INS had been (most appropriately?) part of Department of Labor, before it became part of the Department of Justice.
So effectively the creation of DHS and ICE was a way of creating a quasi military "security" force devoted to immigration** and get it away from the more broadly focused Department of Justice (DOJ) which might actually be concerned about civil rights, etc. The FBI is part of the DOJ and has a better reputation for professionalism than ICE.
No less than the American Friends Service Committee calls for the Abolition of ICE on those grounds.
On January 30, 2026 was the congressional move to separate ICE funding (a mind boggling $170 Billion) from the rest of the budget a good strategy for reforming or abolishing ICE, or a strategy for face saving of top Democrats who have in fact long favored big ICE funding increases themselves? I don't know, I've seen both opinions.
Who are the undocumented immigrants in the US? They come from any countries which used to be led by Mexico, though recently more Mexicans have been leaving the US than coming to it. More recently undocumented immigration has been dominated by influx from broken Central American countries, which the US had a large hand in breaking.
When did these immigrants come to the US? Most undocumented immigrants in the US came here a long time ago. The undocumented population of the US grew from 3.5 million in 1990 on a steady ramp upwards through the Presidencies of Bill Clinton and GW Bush peaking before the Global Financial Crisis at 12.2 million then slowly falling during the Obama administration (who did record numbers of deporations) to 10.2 million, then gradually rising with an extra boost of Central Americans in 2023 to about 13 million. I would call this trajectory basically horizontal since 2008, and while buffeted by external events shows no consistent differences between Democrat and Republican Presidents.
The states that most undocumented immigrants go to is also neither Blue nor Red States but both. California and Illinois and two leading Blue states for undocumented immigrants, as are Red states Texas and Florida. Hardly any undocumented immigrants go to most states.
(*Count me among those who believe that the 9/11 was not carried out by government agents as 9/11 Truthers assert, but allowed to happen both through the evil designs of necons like Dick Cheney and GW Bush, and the incompetence of appointees like Donald Rumsfeld. This makes me doubly suspicious of any laws that were inspired by it, like the infamous Patriot Act which is well known to have long been in the works, just like the War in Iraq.)
(**Supposedly devoted to immigration anyway. They seem to have taken up an unspoken political mission of quashing dissent to the fascist politics of President Trump, operating something like Gestapo or Brown Shirts.)