Federal law enforcement officials said they were investigating a series of letters mailed to members of Congress and secretaries of state in recent days.

© Tierney L. Cross for The New York Times

A New York Times analysis of Senator Susan Collins’s voting record shows that she frequently breaks with Republicans but more seldom changes an outcome.

© Haiyun Jiang/The New York Times

Tipped workers in Arizona have benefited from the G.O.P.’s big tax cut. But they face economic stress from other Republican policies.

© Anna Watts for The New York Times