At their new political high-water mark, Republicans have plenty of reasons to celebrate - and at least one large cause for worry. On Election Day, voters shattered the Obama agenda of expanded public benefits and increased income tax progressivity, leaving the president to reassemble his goals with glue and tape. During this midterm cycle, Republicans became reacquainted with estranged friends: independents, seniors, college-educated voters, working-class voters, rural voters and suburban voters. The Republican Party will benefit from the infusion of diverse, attractive new leaders, including some, such as Florida Sen.-elect Marco Rubio, with Tea Party pedigrees...