The gatherings, described by a half-dozen administration officials and Republicans close to the administration, have taken shape over time, from loosely structured meetings and conference calls among like-minded officials early in the administration to more formal meetings in recent months. And they have produced the president’s two most controversial policies — the January 2017 travel ban, which the Supreme Court let stand Tuesday, and the more recent decision to send adults caught crossing the border illegally for criminal prosecution, which resulted in thousands of children being separated from their parents and warehoused in government shelters.

The secretive nature of the effort was born of Miller’s assumption that hostile bureaucrats would try to undermine the administration’s aggressive policies before they got off the ground, by leaking to the news media or pushing alternative proposals to senior officials.

But the opacity has had a ripple effect throughout the administration, causing consternation and confusion within the government agencies that have to carry out the policies. Without an organized policy and communications strategy integrating the input of key agencies, senior administration officials have been caught unaware by major policy announcements, and confusion has ensued about how to carry them out, according to administration officials and outside advisers who support Trump’s immigration agenda.