Trump's immigration framework, sent to the Hill late last month, included a path to citizenship for 1.8 million dreamers - more than twice as many as enrolled in DACA.
For Republicans, Trump's willingness to offer a path to citizenship to a much larger group of dreamers meant any Democratic concessions had to go well beyond a border wall.
The president's demands for large cuts to legal family immigration programs and the elimination of the diversity visa lottery were intended to balance out the legalization of the dreamers, the aides said.
Thanks to a push from Trump's hard-line advisers and key lawmakers - and conservative media outlets that amplified threats from "chain migration" and the visa lottery - curbs to legal immigration became a central part of the GOP demands.
"If you would have said at the beginning of President Trump's administration that one year in he is willing to grant a pathway to citizenship for 1.8 million currently illegal immigrants, your jaw would have hit the floor, right? I mean, that is not a concession that is commensurate with a wall," said Josh Holmes, a Republican consultant who is close to Senate Majority Leader Mitch McConnell, R-Ky. "The opportunity here was to do something further than the bare minimum."
The bipartisan plan from the Senate's self-styled "Common Sense Coalition" did not touch the diversity visa program and made relatively minor changes to family immigration rules. But as the "war room" of administration lawyers and policy experts examined the 64-page text on Wednesday, it was a handwritten note on the final page that set off the loudest alarm bells.
That section dealt with setting in law DHS's priorities for enforcement. Under the proposal, the agency would focus its powers on immigrants with felonies or multiple misdemeanors, who were national security threats and who had arrived in the country after a certain date.
Scribbled in the margins was a date: June 30, 2018.
The administration team was dumbstruck: In addition to making it harder for DHS to deport all of those already here illegally, lawmakers were opening the door to a surge of new unauthorized immigrants by setting an effective "amnesty" date four months in the future.
"No one who has worked on immigration issues in the administration or on the Hill was aware of any legislation that had ever been proposed and scheduled to receive a vote on the floor of the Senate that created an amnesty program effectively for those who arrive in the future," said a DHS official who helped lead the review. "That would clearly and unequivocally encourage a massive wave of illegal immigration and visa overstays."