President Trump on Monday was the latest big political star to swing through Mississippi and boost a candidate in a red-state Senate race that suddenly seems competitive.

© Doug Mills/The New York Times

President Trump will stump for a senator in a state he has won three times by double digits, and as Democrats see a path to victory.

© Haiyun Jiang/The New York Times

Farmers and ranchers have supported President Trump for a decade. But the war in Iran, tariffs and other administration policies have soured some on the G.O.P.