A cooperating witness in the special counsel investigation worked for more than a year to turn a top Trump fund-raiser into an instrument of influence at the White House for the rulers of Saudi Arabia and the United Arab Emirates, according to interviews and previously undisclosed documents.

Hundreds of pages of correspondence between the two men reveal an active effort to cultivate President Trump on behalf of the two oil-rich Arab monarchies, both close American allies.

High on the agenda of the two men -- George Nader, a political adviser to the de facto ruler of the U.A.E., and Elliott Broidy, the deputy finance chairman of the Republican National Committee -- was pushing the White House to remove Secretary of State Rex W. Tillerson, backing confrontational approaches to Iran and Qatar and repeatedly pressing the president to meet privately outside the White House with the leader of the U.A.E.

Mr. Tillerson was fired last week, and the president has adopted tough approaches toward both Iran and Qatar.