Top Trump administration officials have pushed to build nuclear power plants throughout Saudi Arabia over the vigorous objections of White House lawyers who question the legality of the plan and the ethics of a venture that could enrich Trump allies, according to a new report by House Democrats. The report is the most detailed portrait to date of how senior White House figures — including Michael T. Flynn, President Trump’s first national security adviser — worked with retired military officers to circumvent the normal policymaking process to promote an export plan that experts worried could spread nuclear weapons technology in the volatile Middle East. Administration lawyers warned that the nuclear exports plan — called the Middle East Marshall Plan — could violate laws meant to stop nuclear proliferation and raised concerns about Mr. Flynn’s conflicts of interest.