The new rules are part of a broad push by the Trump administration to crack down not only on illegal immigration but also to tighten restrictions on legal immigration. Ira Mehlman, a spokesman for the Federation for American Immigration Reform, which generally advocates stricter immigration rules, said his group supported the new rule.“It’s an effort to prevent people from abusing the legal immigration process,” Mr. Mehlman said. “The burden of proof should be on the people who say their plans have changed.