President Donald Trump signed a memorandum on Tuesday that would prevent migrants who are in the United States illegally from being counted when U.S. congressional voting districts are next redrawn, triggering swift rebukes from Democrats and threats of litigation. U.S. census experts and lawyers say the action is legally dubious, and not easily executed in practice. Democratic-led states, including New York, and civil rights groups have already vowed to mount a legal challenge or said they are considering it. If enacted, the plan could benefit Trump’s Republican Party by eliminating the largely non-white population of migrants in the United States illegally, creating voting districts that skew more Caucasian. It could also cause populous states with large immigrant contingents to lose seats in the 435-member U.S. House of Representatives, including big left-leaning states like California - currently with 53 seats - and New York, with 27.