Fred D. Thompson had one central strategic goal as he formally began his presidential campaign on Thursday: to win over conservatives who are disheartened at their current choice of Republican candidates by positioning himself as the ideological and stylistic heir of Ronald Reagan....

Yet in some notable ways, Mr. Thompson is different from Reagan, and he has at times deviated from the orthodox conservatism that Reagan, after his death and nearly two decades removed from his presidency, has come to represent.

Mr. Thompson, the former senator from Tennessee, has at times voted in support of affirmative action, at other times against it; Reagan’s Justice Department consistently championed efforts to eliminate it. Mr. Thompson, a former trial lawyer, has voted against efforts to impose federal caps on punitive damages and lawyers’ fees, a central part of the conservative agenda.